five reasons to eat more dates:

Here are five reasons to eat more dates:

1. Dates are a source of antioxidants. All dates, fresh or dried, contain different types of antioxidants. Fresh dates contain anthocyanidins and carotenoids, while dried dates contain polyphenols – just like green tea. Experiments in food chemistry show that Khalas (aka Madina) dates are highest in antioxidants when compared to other date varieties.

2. Dates can be good for blood sugar balance. Diabetes researchers have shown that dates have a low glycemic impact. This means that eating dates alone, or with a meal, may help people with type-2 diabetes manage their blood sugar and blood fat levels. Six to eight Tamer dates can be eaten in one sitting without dramatic shifts in blood sugar.

3. Dates can help reduce blood pressure. A standard serving of five or six dates provides about 80 milligrams of magnesium, an essential mineral that helps dilate blood vessels. Research shows that supplementing with 370 milligrams of magnesium can reduce blood pressure. However, taking such a large dose all at once often causes diarrhea. Dates are a delicious way to increase your magnesium intake more gently.

4. Dates contain a brain booster. Each little date contains over two milligrams of choline, a B vitamin that’s a component in acetylcholine, the memory neurotransmitter. Higher choline intake is associated with better memory and learning, making it a key nutrient for children and older adults at risk for Alzheimer’s.

5. Dates help maintain bone mass. Research shows that bone loss in post-menopausal women with osteopenia can be reduced by increasing intake of potassium. One dried date provides nearly 140 milligrams of this valuable nutrient. Scientists believe that high potassium intake protects bone mass by reducing the amount of calcium excreted through the kidneys.

Is a zebra white with black stripes or black with white stripes?

What is an owl pellet?

Owls are birds of prey. That means that they hunt the animals that they eat. After an owl eats the small rodents, birds, and bugs that are a part of its nightly diet, its stomach cannot digest the fur, bones, teeth, feathers, and insect shells from that food. These “extra” parts are formed into a tight PELLET inside the owl and are then are later SPIT UP by the owl. Pellets are usually about as big as an adult thumb and they are often dissected by students and scientist to help them learn exactly what owls eat and what kinds of small animals and bugs live in a particular area. If you get a chance to examine what is inside an owl pellet, you will be lucky, there is a lot to learn and it is surprisingly FUN!

Is a zebra white with black stripes or black with white stripes?

So, is a zebra white with black stripes or black with white stripes? Unfortunately, there is no true answer to this perplexing question. The reason is because the answer to this question comes down to a person’s perspective. Many zoologists would say that a zebra is white because its stripes end towards the belly and the belly is mostly white. Others would say that a zebra is black because if you shaved all the fur off a zebra the skin is, surprisingly,  mostly black. So the answer actually depends on who you ask and how you want to look at a zebra.

integer

Question 1.

Evaluate the following, using the number line:

(i) 4 – (-2)

(ii) -4 – (-2)

(iii) 3 – 6

(iv) -3 – (-5)

Solution:

(i) Start from 4 on the number line.

Move 2 units to the digits we reach at 6

∴ 4 – (-2) = 4 + 2 = 6

 

(ii) Start from -4 on the number line.

Move 2 units to the right, we reach at -2

∴ -4 – (-2) = —4 + 2 = -2

(iii) Start from 3 on the number line.

Move 6 units to the left, we reach at -3

3 – 6 = -3

(iv) Start from -3 on the number line.

Move 5 units to the right, we reach at 2

-3 – (-5) = -3 + 5 = 2

Question 2.

Subtract :

(i) -6 from 9

(ii) 6 from -9

(iii) -6 from -9

(iv) -725 from -63

(v) -376 from 10

(vi) 92 from -620

Solution:

(i) 9 – (-6) = 9 + 6 = 15

(ii) -9 – 6 = -15

(iii) -9 – (-6) = -9 + 6 = -3

(iv) -63 – (-725) = -63 + 725 = +662

(v) 10 – (-376) = 10 + 376 = 386

(vi) -620 – 92 = -712

Question 3.

Evaluate the following:

(i) -237 – (+ 1884)

(ii) -346 – (- 1275)

(iii) -190 – (-3512)

(iv) -2718 – (+ 6827)

Solution:

(i) -237 – (+ 1884)

= -237 – 1884

= -(237 + 1884) = -2121

 

(ii) -346 -(- 1275)

= -346 + 1275

= 1275 – 346 = 929

(iii) -190 – (-3512)

= -190 + 3512

= 3512- 190 = 3322

(iv) 2718 – (+ 6827)

= -2718 – 6827

= -(2718 + 6827) = -9545

Question 4.

The sum of two integers is 17. If one of them is -35, find the other.

Solution:

One number = -35

Sum of two integers =17

Second number = Sum of integers – (The given number)

= 17 – (-35)

= 17 + 35 = 52

Question 5.

What must be added to -23 to get -9?

Solution:

Let the number to be added = x

∴ -23 + x = -9

∴ The required number = -9 – (-23)

= -9 + 23 = 14

Question 6.

Find the predecessor of 0.

Solution:

Predecessor of 0 = 0 – 1 = -1

Question 7.

Find the successor and the predecessor of the following integers:

(i) -31

(ii) -735

(iii) -240

Solution:

(i) Successor of -31 = -31 + 1 = -30

Predecessor of -31 = -31 – 1 = -32

(ii) Successor of -735 = -735 + 1 = -734

Predecessor of-735 = -735 – 1 = -736

(iii) Successor of -240 = -240 + 1 = -239

Predecessor of -240 = -240 – 1 = -241

Question 1.

Find the value of:

(i) 6 – 9 + 4

(ii) -5 – (-3) + 2

(iii) 7 + (-5) + (-6)

(iv) 6 – 3 – (-5)

Solution:

(i) 6 – 9 + 4

= (6 + 4) – 9 = 10 – 9= 1

 

(ii) -5 – (-3) + 2

= -5 + 3 + 2 = -5 + 5 = 0

(iii) 7 + (-5) + (-6)

= 7 – 5 – 6 = 2 – 6 = -4

(iv) 6 – 3 – (-5)

= 6 – 3 + 5 = 8

Question 2.

Evaluate the following:

(i) -77 + (-84) + 318

(ii) 54 + (-218) – (-76)

(iii) -121 – (-78) + (-193) + 576

(iv) -65 + (-76) – (-28) + 32

Solution:

(i) -77 + (- 84) + 318

= -77 – 84 + 318

= -(77 + 84)+ 318

= -(161) + 318

= -161 +318

= 318 – 161 = 157

(ii) 54 + (-218) – (-76)

= 54 – 218 + 76

= (54 + 76) – 218

= 130 – 218 = – 88

(iii) -121 – (-78) + (-193) + 576

= -121 + 78 – 193 + 576

= -121 – 193 + 78 + 576

= -(121 + 193) + 78 + 576

= -(314) + 654

= 654 – 314 = 340

(iv) -65 + (-76) – (-28) + 32

= -65 – 76 + 28 + 32

= -(65 + 76) + 60

= -141 + 60 = -81

Question 3.

Find the value of:

(i) 8 – 6 + (-2) – (-3) + 1

(ii) 31 + (-23) – 35 + 18 – 4 – (-3)

Solution:

(i) 8 – 6 + (-2) – (-3) + 1

= 8 – 6 – 2 + 3 + 1

=-6 – 2 + 8 + 3 + 1

= -6 – 2 + 12

=-8 + 12 = 4

(ii) 31 + (-23) – 35 + 18 – 4 – (-3)

= 31 – 23 – 35 + 18 – 4 + 3

= -23 – 35 – 4 + 31 + 18 + 3

= -23 – 35 – 4 + 52

= -62 + 52 = -10

Question 4.

Rashmi deposited ₹ 4370 in her account on Monday and then withdrew ₹ 2875 on Tuesday. Next day she deposited ₹ 1550. What was her balance on Thursday?

Solution:

Rashmi deposited in her account on Monday = ₹ 4370

Less withdrawal on Tuesday = ₹ 2875

So the Balance on Tuesday

= ₹ 4370 – ₹ 2875

= ₹ 1495

Again she deposited on Wednesday = ₹ 1550

Balance on Thursday

= ₹ 1495 + ₹ 1550 = ₹ 3045

🍓🍓🍓🍓🍓🍓🍓🍓🍓🍓🍓🥕🥕🥕🥕

Question 1.

Use the appropriate symbol < or > to fill in the following blanks:

(i) (-3 + ……… (-6) (-3) – (-6)

(ii) (-21) – (-10) ……. (-31)+ (-11)

(iii) 45 – (-11) ……….. (57) + (-4)

(iv) (-25) – (-42) …………. (-42) – (-25)

Solution:

(i) (-3 + (-6) < (-3) – (-6)

(ii) (-21) – (-10) > (-31) + (-11)

(iii) 45 – (-11) > (57) +(-4)

(iv) (-25 – (-42) > (-42) – (-25)

Question 2.

Find the value of:

(i) 12 + ( -3) + 5 – (-2)

(ii) 39 – 35 + 7-(-4) + 21

(iii) -15- (-2) – 71 – 8 + 6

Solution:

(i) 12 + (-3) + 5 – (-2)

= 12 – 3 + 5 + 2

= 9 + 7= 16

(ii) 39 – 35 + 7 – (-4) + 21

= 39 – 35 + 7 + 4 + 21

= 4 + 11 + 21

= 15 + 21 =36

(iii) -15 – (-2) – 71 – 8 + 6

= -15 + 2 – 71 – 8 + 6

= -13 – 79 + 6

= 92 + 6 = -86

Question 3.

Evaluate:

(i) |-13| – |-15|

(ii) |35 – 41| – |7-(-2)|

Solution:

(i) |-13| – |-15|

= +13 – 15 =-2

(ii) |35 – 41| – |7 – (-2)|

= 6 – 9 = -3

Question 4.

Arrange the following integers in ascending order:

-39, 35, -102, 0, -51, -5, -6, 7

Solution:

-102, -51, -39, -6, -5, 0, 7, 35

Question 5.

Find the successor and the predecessor of -199.

Solution:

Successor = -199 – 1 = -198

Predecessor = -199 – 1 = -200

Question 6.

Subtract the sum of -235 and 137 from -152.

Solution:

Sum of (-235 and 137)

= -235 + 137

= 137 – 235 = -98

Now, subtract the sum of (-235 and 137) from -152

= 152 – (-98)

= -152 + 98 = -54

Question 7.

What must be added to -176 to get -95?

Solution:

Let the number to be added = x

∴ -176 + x = -95

x = -95 + 176 = 81

Question 8.

What is the difference in height between a point 270 m above sea level and 80 m below sea level?

Solution:

Height above sea level = +270 m

Height below sea level = -80 m

Difference = +270 – (-80)

= 270 + 80 = 350 m

whole number

🍑🍑🍑🍑🍑🍑

Question 1.

Fill in the blanks to make each of the following a true statement:

(i) 378 + 1024 = 1024 + …….

(ii) 337 + (528 + 1164) = (337 + ……..) + 1164

(iii) (21 + 18) + ……….. = (21 + 13) + 18

(iv) 3056 + 0 = ……….. = 0 + 3056

Solution:

(i) 378 + 1024= 1024 + 378 (Commutative property of addition)

(ii) 337 + (528 + 1164) = (337 + 528) + 1164 (Associative law of addition)

(iii) (21 + 18) + 13 = (21 + 13) + 18 (Associative law of addition)

(iv) 3056 + 0 = 3056 = 0 + 3056

 

Question 2.

Add the following numbers and check by reversing the order of addends :

(i) 3189 + 53885

(ii) 33789 + 50311.

Solution:

(i) 3189 + 53885 = 57074

Check 53885 + 3189 = 57074

∴57074

(ii) 33789 + 50311 = 84100

Check 50311 + 33789 = 84100

∴ 84100

Question 3.

By suitable arrangements, find the sum of:

(i) 311,528,289

(ii) 723, 834, 66, 277

(iii) 78, 203, 435, 7197, 422.

Solution:

(i) 311, 528, 289

Sum (311 +289)+ 528

= 600+ 528= 1128

(ii) 723 + 834 + 66 + 277

= (723 + 277) + (834 + 66)

= 1000 + 900 = 1900

(iii) 78, 203, 435, 7197, 422

Sum = (78 + 422) + (203 + 7197) + 435

= 500 + 7400 + 435

= 7900 + 435 = 8335

 

Question 4.

Fill in the blanks to make each of the following a true statement:

(i) 375 × 57 = 57 × ……….

(ii) (33 × 16) × 25 = 33 × (…….. × 25)

(iii) 37 × 24 = 37 × 18 + 37 × …………

(iv) 7205 × 1 = …………. = 1 × 7205

(v) 366 × 0 =

(vi) …………… × 579 = 0

(vii) 473 × 108 = 473 × 100 + 473 × ………….

(viii) 684 × 97 = 684 × 100 – …………… × 3

(ix) 0 ÷= 5 =

(x) (14 – 14) ÷ 7 = ………….

Solution:

(i) 375 × 57 = 57 × 375 (Commutative property of multiplication)

(ii) 33 × 16) × 25 = 33 × (16 × 25) (Associative law of multiplication)

(iii) 37 × 24 = 37 × 18 + 37 × 6 (Distributive law of multiplication)

(iv) 7205 × 1 = 7205 = 1 × 7205

(v) 366 × 0 = 0

(vi) 0 × 579 = 0

(vii) 473 × 108 = 473 × 100 + 473 × 8

(viii) 684 × 97 = 684 × 100 – 684 × 3

(ix) 0 ÷ 5 = 0

(x) (14 – 14) ÷ 7 = 0

Question 5.

Determine the following products by suitable arrangement:

(i) 4 × 528 × 25

(ii) 625 × 239 × 16

(iii) 125 × 40 × 8 × 25

Solution:

(i) 4 × 528 × 25 = 4 × 25 × 528

= 100 × 528 = 52800

(ii) 625 × 239 × 16 = 625 × 16 × 239

= 10000 × 239 = 2390000

(iii) 125 × 40 × 8 × 25 = 125 × 8 × 40 × 25

= 1000 × 1000 = 1000000

Question 6.

Find the value of the following:

(i) 54279 × 92 + 54279 × 8

(ii) 60678 × 262 – 60678 × 162

Solution:

(i) 54279 × 92 + 54279 × 8

= 54279 (92 + 8)

= 54279 × 100 = 5427900

 

(ii) 60678 × 262 – 60678 × 162

= 60678 (262 – 162)

= 60678 × 100 = 6067800

Question 7.

Find the following products by using suitable properties:

(i) 739 × 102

(ii) 1938 × 99

(iii) 1005 × 188

Solution:

(i) 739 × 102

= 739 × (100 + 2)

= 739 × 100 + 739 × 2

= 73900 + 1478 = 75378

(ii) 1938 × 99

= 1938 × (100- 1)

= 1938 × 100 – 1938 × 1

= 193800 – 1938 = 191862

(iii) 1005 × 188

= (1000 + 5) × (100 + 88)

= 1000 × 100 + 1000 × 88 + 5 × 100 + 88 × 5

= 100000 + 88000 + 500 + 440 = 188940

Question 8.

Divide 7750 by 17 and check the result by division algorithm.

Solution:

7750 ÷ 17

On dividing 7750 by 17, we get

Quotient = 455 and Remainder = 15

Check by division algorithm:

Divident = Divisior × Quotient + Remainder

= 17 × 455 + 15 = 7750

Question 9.

Find the number which when divided by 38 gives the quotient 23 and remainder 17.

Solution:

Divisor = 38,Quotient = 23

Remainder = 17

Dividend = divisor × quotient + remainder

= 38 × 23 + 17 = 874 + 17 = 891

 

Question 10.

Which least number should be subtracted from 1000 so that the difference is exactly divisible by 35.

Solution:

On dividing 1000 by 35

we get quotient = 28 and remainder 20

So, 20 should be subtracted from 1000.

Question 11.

Which least number should be added to 1000 so that 53 divides the sum exactly.

Solution:

On dividing 1000 by 53, we get quotient = 18 and remainder = 46. To get the remainder 0, we should add 53 – 46 = 7 to 1000.

∴ 7

Question 12.

Find the largest three-digit number which is exactly divisible by 47.

Solution:

Largest three digit no. = 999

On dividing 999 by 47, we get

Quotient = 21 and Remainder =12

So on subtracting 12 from 999, we get

999 – 12 = 987

Question 13.

Find the smallest five-digit number which is exactly divisible by 254.

Solution:

Smallest 5 digit number = 10000

On dividing 10000 by 254, we get

Remainder = 94

So 254 – 94 = 160 should be added to 10000 to get the smallest 5 digit number divisible by 254.

∴ 10000 + 160 = 10160

Question 14.

A vendor supplies 72 litres of milk to a student’s hostel in the morning and 28 litres of milk in the evening every day. If the milk costs?39 per litre, how much money is due to the vendor per day?

Solution:

Supply of milk in morning = 72 litres

Supply of milk in evening = 28 litres

Cost of per litre milk = ₹ 39

Money of per day = ₹ 39 (72 l + 28 l)

= ₹ 39 × 100 = ₹ 3900

Question 15.

State whether the following statements are true (T) or false (F):

(i) If the product of two whole numbers is zero, then atleast one of them will be zero.

(ii) If the product of two whole numbers is 1, then each of them must be equal to 1.

(iii) If a and b are whole numbers such that a ≠ 0 and b ≠ 0, then ab may be zero.

Solution:

(i) True

(ii) True

(iii)False

🍒🍒🍒🍒🍒🍒🍒🍒🍒🍒🍒🍒🍒🍒🍒

Question 1.

Using shorter method, find

(i) 3246 + 9999

(ii) 7501 + 99999

(iii) 5377 – 999

(iv) 25718 – 9999

(v) 123 × 999

(vi) 203 × 9999

Solution:

(i) 3246 + 9999

= (3246 – 1) + (9999 + 1) (Adding and subtracting 1)

= 3245 + 10000 = 13245

 

(ii) 7501 + 99999

= (7501 – 1) + (99999 + 1) (Adding and subtracting 1)

= 7500+ 100000 = 107500

(iii) 5377 – 999

= 5377 – (1000- 1)

= 5377 – 1000 + 1 = 4377 + 1 = 4378

(iv) 25718 – 9999

= 25718 – (10,000 – 1)

= 15718 + 1 = 15719

(v) 123 × 999

= 123 × (1000 – 1) (By subtracting 1)

= 123 × 1000 – 1 × 123 = 123000 – 123 = 122877

(vi) 203 × 9999

= 203 × (10,000 – 1) (By subtracting 1)

= 203 × 10,000 – 203 × 1 = 2030000 – 203 = 2029797

 

Question 2.

Without using a diagram, find

(i) 9th square number

(ii) 7th triangular number

Solution:

(i) 9th square number = ?

The first square number is 1 × 1 = 1

The second square number is 2 × 2 = 4

The third square number is 3 × 3 = 9

Similarly 9th square number is 9 × 9 = 81

(ii) 7th triangular number = ?

First triangular number = 1

Second triangular number = 1 + 2 = 3

Third triangular number = 1 + 2 + 3 = 6

Fourth triangular number = 1 + 2 + 3 + 4 = 10

Similarly 7th triangular number = 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28

Question 3.

(i) Can a rectangular number be a square number?

(ii) Can a triangular number be a square number?

Solution:

(i) Yes, 9 is a square as well as rectangular number.

(ii) Yes, 8th triangular number = 36, which is a square number.

Question 4.

Observe the following pattern and fill in the blanks:

1 × 9 + 1 = 10

12 × 9 + 2= 110

123 × 9 + 3 = 1110

1234 × 9 + 4 = ……….

12345 × 9 + 5 = …………..

Solution:

1 × 9 + 1 = 10

12 × 9 + 2= 110

123 × 9 + 3 = 1110

1234 × 9 + 4 = 11110

12345 × 9 + 5 = 111110

Question 5.

Observe the following pattern and fill in the blanks:

9 × 9 + 7 = 88

98 × 9 + 6 = 888

987 × 9 + 5 = 8888

9876 x 9 + 4 = …………

98765 × 9 + 3 = ……….

Solution:

9 × 9 + 7 = 88

98 × 9 + 6 = 888

987 × 9 + 5 = 8888

9876 × 9 + 4 = 88888

98765 × 9 + 3 = 888888

🍓🍓🍓🍓🍓🍓🍓🍓🍓🍓🍓🍓🍓

Question 1.

Write next three consecutive whole numbers of the number 9998.

Solution:

The next three consecutive whole number of 9998 are:

9998 + 1 = 9999

9999 + 1 = 10000

10000 + 1 = 10001

∴ Numbers are = 9999, 10000, 10001

 

Question 2.

Write three consecutive whole numbers occurring just before 567890.

Solution:

The three consecutive whole numbers just before 567890 are:

567890 – 1 = 567889 – 1 = 567888 – 1

= 567887

∴ These are : 567889, 567888, 567887

Question 3.

Find the product of the successor and the predecessor of the smallest number of 3-digits.

Solution:

Smallest number of 3-digits = 100

Successor = 100 + 1

Predecessor =100 – 1

∴ Product = 100 + 1 × 100 – 1

= 101 × 99 = 9999

Question 4.

Find the number of whole numbers between the smallest and the greatest numbers of 2-digits.

Solution:

Smallest number of 2-digits = 10

Greatest number of 2-digits = 99

Numbers between 10 and 99

11, 12, …………, 98

= 98 – 10 = 88

Question 5.

Find the following sum by suitable arrangements:

(i) 678 + 1319 + 322 + 5681

(ii) 777 + 546 + 1463 + 223 + 537

Solution:

(i) 678 + 1319 + 322 + 5681

= (678 + 322) + (5681 + 1319)

= 1000 + 7000 = 8000

(ii) 777 + 546 + 1463 + 223 + 537

= (777 + 223) + (1463 + 537) + 546

= 1000 + 2000 + 546 = 3546

 

Question 6.

Determine the following products by suitable arrangements:

(i) 625 × 437 × 16

(ii) 309 × 25 × 7 × 8

Solution:

(i) 625 × 437 × 16

= 437 × (625 × 16)

= 437 × 10000 = 4370000

(ii) 309 × 25 × 7 × 8

= (309 × 7) × (25 × 8)

= 2163 × 200 = 432600

Question 7.

Find the value of the following by using suitable properties:

(i) 236 × 414 + 236 × 563 + 236 × 23

(ii) 370 × 1587 – 37 × 10 × 587

Solution:

(i) 236 × 414 + 236 × 563 + 236 × 23

= 236 × (414 + 563 + 23)

= 236 × (1000) = 236000

(ii) 370 × 1587 – 37 × 10 × 587

= 37 × 10(1587 – 587)

= 370 × 1000 = 370000

Question 8.

Divide 6528 by 29 and check the result by division algorithm.

Solution:

6528 ÷ 29

∴ Quotient = 225

and Remainder = 3

Question 9.

Find the greatest 4-digit number which is exactly divisible by 357.

Solution:

Largest 4 digit number is 9999

Dividing 9999 by 357, we get

Remainder = 3

Subtracting 3 from 9999, 9999 – 3 = 9996,

we get the required number divisible by 357.

So 9996

Question 10.

Find the smallest 5-digit number which is exactly divisible by 279.

Solution:

Smallest 5-digit number is 10000

Dividing it by 279, we get remainder = 235

To make the smallest 5-digit number exactly divisible by 279, we have to add 279 – 235 = 44 in 10000

∴ 10000 + 44 = 10044.

Icse class 6 chapter 1 math

🥒🍇🍌🍍

Question 1.

Round off each of the following numbers to their nearest tens:

(i) 77

(ii) 903

(iii) 70 1205

(iv) 999

Solution:

(i) 77

The digit at unit place is 7, which is greater than 5.

Hence, the rounded off number to nearest tens = 80.

 

(ii) 903

The digit at unit place is 3, which is less than 5.

Hence, the rounded off number to nearest tens = 900.

(iii) 1205

The digit at unit place is 5, which is equal to 5.

Hence, the rounded off number to nearest tens = 1210

(iv) 999

The digit at unit place is 9, which is greater than 5.

Hence, the rounded off number to nearest tens = 1000.

Question 2.

Estimate each of the following numbers to their nearest hundreds:

(i) 1246

(ii) 32057

(iii) 53961

(iv) 555555

Solution:

(i) 1246

The digit at tens place is 4, which is less than 5.

Hence, the rounded off number to nearest hundreds = 1200.

(ii) 32057

The digit at tens place is 5, which is equal to 5.

Hence, the rounded off number to nearest hundreds = 32100.

 

(iii) 53961

The digit at tens place is 6, which is greater than 5.

Hence, the rounded off number to nearest hundreds = 54000.

(iv) 555555

The digit at tens place is 5, which is equal to 5.

Hence, the rounded off number to nearest hundreds = 555600.

Question 3.

Estimate each of the following numbers to their nearest thousands:

(i) 5706

(ii) 378

(iii) 47,599

(iv) 1,09,736

Solution:

(i) 5706

The digit at hundred place is 7, which is greater than 5.

Hence, the rounded off number to nearest thounsands = 6000.

(ii) 378

The digit at hundred place is 3, which is less than 5.

Hence, the rounded off number to nearest thousands = 0.

(iii) 47,599

The digit at hundred place is 5, which is equal to 5.

Hence, the rounded off number to nearest thousands = 48000.

(iv) 1,09,736

The digit at hundred place is 7, which is greater than 5.

Hence, the rounded off number to nearest thousands = 1,10,000.

Question 4.

Give a rough estimate (by rounding off to nearest hundreds) and also a closer estimate (by rounding off to nearest tens):

(i) 439 + 334 + 4317

(ii) 8325 – 491

(iii) 1,08,734-47,599

(iv) 4,89,348 – 48,365

Solution:

(i) Rounding off to nearest hundreds 439 + 334 + 4317

= 400 + 300 + 4300 = 5000 Rounding off to nearest tens 439 + 334 + 4317

= 440 + 330 + 4320 = 5090

 

(ii) Rounding off to nearest hundreds 8325 – 491

= 8300 – 500 = 7800 Rounding off to nearest tens 8325 – 491

= 8330 – 490 = 7840

(iii) 1,08,734 – 47,599

Rounding off to nearest hundreds 1,08,734 – 47,599

= 1,08,700 – 47,600 = 61,100 Rounding off to nearest tens 1,08,734 – 47,599

= 1,08,730 – 47,600 = 61,130

(iv) 4,89,348 – 48,365

Rounding off to nearest hundreds 4,89,348 – 48,365

= 4,89,300 – 48,400 = 4,40,900 Rounding off to nearest tens 4,89,348 – 48,365

= 4,89,350 – 48,370 = 4,40,980

Question 5.

Estimate each of the following by rounding off each number nearest to its greatest place:

(i) 730 + 998

(ii) 5,290 + 17,986

(iii) 796-314

(iv) 28,292 – 21,496

Solution:

(i) 730 + 998

Rounding off 730 to its greatest place i.e. hundred place = 700

Rounding off 998 to its greatest place i.e. hundreds place = 1000

Hence, estimated sum = 700 + 1000 = 1700

(ii) 5,290 + 17,986

Rounding off 5,290 to its greatest place i.e. thousands place = 5000

Rounding off 17,986 to its greatest place i. e. thousands place = 18,000 Hence, estimated sum = 5,000 + 18,000 = 23,000

(iii) 796 – 314

Rounding off 796 to its greatest place i.e. hundreds place = 800 Rounding off 314 to its greatest place i.e. hundreds place = 300 Hence, estimated difference = 800 – 300 = 500

 

(iv) 28,292 – 21,496

Rounding off28,292 to its greatest place i.e. thousands place = 28,000 Rounding off 21,496 to its greatest place i. e. thousands place = 21,000 Hence, estimated difference = 28,000 – 21,000 = 7,000

Question 6.

Estimate the following products by rounding off each of its factors nearest to its greatest place:

(i) 578 × 161

(ii) 9650 × 27

Solution:

(i) 578 × 161

Rounding off 578 to its greatest place i.e. hundreds place = 600

Rounding off 161 to its greatest place i.e. hundreds place = 200

Hence, estimated product = 600 x 200 = 1,20,000

(ii) 9650 × 27

Rounding off 9650 to its greatest place i.e. thousands place = 10000

Rounding off 27 to its greatest place i.e. tens place = 30

Hence, estimated product = 10000 × 30 = 3,00,000

Question 7.

Estimate the following products by rounding off each of its factors nearest to its hundreds place:

(i) 5281 × 3491

(ii) 1387 × 888

Solution:

(i) 5281 x 3491

Rounding off 5281 to its hundreds place = 5300

Rounding off 3491 to its hundreds = 3500

Hence, estimated product = 5300 × 3500 = 1,85,50,000

(ii) 1387 × 888

Rounding off 1387 to its hundreds place = 1400

Rounding off 888 to its hundreds place = 900

Hence, estimated product = 1400 × 900 = 12,60,000

ML Aggarwal Class 6 Solutions for ICSE Maths Chapter 1 Knowing Our Numbers Objective Type Questions

Mental Maths

Question 1.

Fill in the blanks:

(i) The digit …………… has the highest place value in the number 2309.

(ii) The digit …………… has the highest face value in the number 2039.

(iii) The digit …………… has the lowest place value in the number 2039.

(iv) Both Indian and International systems of numeration have …………… period in common.

(v) In the International system of numeration, commas are placed from …………… after every …………… digits.

(vi) The bigger number from the numbers 57,631 and 57,361 is ……………

(vii) 1 crore = …………… million

(viii)The smallest 4-digit number with 3 different digits is ……………

(ix) The greatest 4-digit number with 3 different digits is ……………

(x) 15 km 300 m = …………… m

(xi) 7850 cm = …………… m …………… cm

(xii) The number 5079 when estimated to the nearest hundreds is ……………

Solution:

(i) The digit 2 has the highest place value in the number 2309.

(ii) The digit 9 has the highest face value in the number 2039.

(iii) The digit 0 has the lowest place value in the number 2039.

(iv) Both Indian and International systems of numeration have ones period in common.

(v) In the International system of numeration, commas are placed from right after every 3 digits.

(vi) The bigger number from the numbers 57,631 and 57,361 is 57,631.

(vii) 1 crore = 10 million (viii)The smallest 4-digit number with 3 different digits is 1002.

(ix) The greatest 4-digit number with 3 different digits is 9987.

(x) 15 km 300 m = 15300 m

(xi) 7850 cm = 78 m 50 cm

(xii) The number 5079 when estimated to the nearest hundreds is 5100.

 

Question 2.

State whether the following statements are true (T) or false (F):

(i) The difference between the place value and the face of the digit 7 in the number 2701 is 693.

(ii) The smallest 4-digit number -1 = the greatest 3-digit number.

(iii) The place of a digit is independent of whether the number is written in the Indian system or International system of numeration.

(iv) In the International system, a number having less number of digits is always smaller than the number having more number of digits.

(v) The estimated value of 9999 to the nearest tens is 10000.

Solution:

(i) The difference between the place value and the face of the digit 7 in the number 2701 is 693. True

(ii) The smallest 4-digit number-1 = the greatest 3-digit number. True

(iii) The place of a digit is independent of whether the number is written in the Indian system or International system of numeration.

True

(iv) In the International system, a number having less number of digits is always smaller than the number having more number of digits.

True

(v) The estimated value of 9999 to the nearest

Question 2.

State whether the following statements are true (T) or false (F):

(i) The difference between the place value and the face of the digit 7 in the number 2701 is 693.

(ii) The smallest 4-digit number -1 = the greatest 3-digit number.

(iii) The place of a digit is independent of whether the number is written in the Indian system or International system of numeration.

(iv) In the International system, a number having less number of digits is always smaller than the number having more number of digits.

(v) The estimated value of 9999 to the nearest tens is 10000.

Solution:

(i) The difference between the place value and the face of the digit 7 in the number 2701 is 693. True

(ii) The smallest 4-digit number-1 = the greatest 3-digit number. True

(iii) The place of a digit is independent of whether the number is written in the Indian system or International system of numeration.

True

(iv) In the International system, a number having less number of digits is always smaller than the number having more number of digits.

True

(v) The estimated value of 9999 to the nearest

Multiple Choice Questions

Choose the correct answer from the given four options (3 to 17):

Question 3.

The face value of the digit 5 in the number 36503 is

(a) 5

(b) 503

(c) 500

(d) none of these

Solution:

The place value of 5 at hundred’s place

= 5 × 100 = 500 (c)

Question 4.

The difference between the place values of 6 and 3 in 76834 is

(a) 3

(b) 5700

(c) 5930

(d) 5970

Solution:

The place value of 6 at thousand’s place

= 6 × 1000 = 6,000

The place value of 3 at ten’s place

= 3 × 10 = 30

The difference between the place value of 6 and 3 = 6000 – 30 = 5970 (d)

Question 5.

The sum of the place values of all the digits in 5003 is

(a) 8

(b) 53

(c) 5003

(d) 8000

Solution:

The place value of 3 at one’s place

=3 × 1 = 3

The place value of 0 at ten’s place = 0 × 10 = 0

The place value of 0 at hundred’s place = 0 × 100 = 0

The place value of 5 at thousand’s place = 5 × 1000 = 5000

The sum of the place value of all the digits

in 5003 = 3 + 0 + 0 + 5000 = 5003 (c)

 

Question 6.

The total number of 4-digit numbers is

(a) 9000

(b) 9999

(c) 10000

(d) none of these

Solution:

The greatest 3-digit number = 999 The greatest 4-digit number = 9999 .’. The total number of 4-digit numbers

= 9999 – 999 = 9000 (a)

Question 7.

The product of the place values of two-threes in 73532 is

(a) 9000

(b) 90000

(c) 99000

(d) 1000

Solution:

The place value of 3 at ten’s place = 3 × 10 = 30

The place value of 3 at thousand’s place = 3 × 1000 = 3000

The product of place value of two threes = 30 × 3000 = 90000 (b)

Question 8.

The smallest 4-digit number having distinct digits is

(a) 1234

(b) 1023

(c) 1002

(d) 3210

Solution:

The smallest 4-digit number having distinct digits is 1002. (c)

Question 9.

The largest 4-digit number having distinct digits is

(a) 9999

(b) 9867

(c) 9786

(d) 9876

Solution:

The largest 4-digit number having distinct digits is 9867. (b)

 

Question 10.

The largest 4-digit number is

(a) 9999

(b) 9876

(c) 9990

(d) none of these

Solution:

The largest 4-digit number is 9999. (a)

Question 11.

The difference between the largest number of 3-digit and the largest number of 3-digit with distinct digits is

(a) 0

(b) 10

(c) 12

(d) 14

Solution:

The largest number of 3-digit = 999

The largest number of 3-digit with distinct digits = 987

∴ Their difference = 999 – 987 = 12 (c)

Question 12.

If we write natural numbers from 1 to 100, the number of times the digit 5 has been written is

(a) 11

(b) 15

(c) 19

(d) 20

Solution:

If we write natural numbers from 1 to 100, the number of times the digit 5 has been written is 20. (d)

Question 13.

The number 28,549 when rounded off to the nearest hundreds is

(a) 28,000

(b) 28,500

(c) 28,600

(d) 29,000

Solution:

28,549

The digit at tens place is 4, which is less than 5.

Hence, the rounded off number to nearest hundreds = 28,500. (b)

Question 14.

The smallest natural number which when rounded off to the nearest hundreds as 500 is

(a) 499

(b) 501

(c) 450

(d) 549

Solution:

The smallest natural number which when rounded off to the nearest hundreds as 500 is 450. (c)

This is so because the digit at tens place is 5, which is equal to 5.

Question 15.

The greatest natural number which when rounded off to the nearest hundreds as 500 is

(a) 549

(b) 599

(c) 450

(d) none of these

Solution:

The greatest natural number which when rounded off to the nearest hundreds as 500 is 549. (a)

This is so because the digit at tens place is 4, which is less than 5.

Question 16.

The greatest 5-digit number formed by the digits 3, 0, 7 is

(a) 33077

(b) 77730

(c) 77330

(d) none of these

Solution:

The greatest 5-digit number formed by the digits 3, 0, 7 is 77730. (b)

Question 17.

In the International place value system, we write 1 billion for

(a) 10 lakh

(b) 1 crore

(c) 10 crore

(d) 100 crore

Solution:

In the International place value system, we write 1 billion for 100 crore. (d)

Value Based Questions

🥜🥜🥜🥜🥜🥜🥜🥜🥜

Question 1.

The distance between Anu’s home and her school is 4 km 850 m. Everyday she cycles both ways. Find the distance covered by her in a week. (Sunday being a holiday).

What are the advantages of cycling?

Solution:

Distance between Anu’s home and her school = 4 km 850 m = 4 x 1000+ 850 = 4850 m Distance travelled by Anu per day = 4850 m x 2 = 9700 m Since, in a week there are 7 days but Sunday is off.

Hence, distance travelled by Anu for 6 days (a week) = 9700 × 6 = 58200 m

= 58 km 200 m

Cycling is good for health and it saves fuel and helps in reducing pollution.

🍉🍉🍉🍉🍉🍉🍉🍉🍉🍉🍉🍉🍉🍉🍉

Higher Order Thinking Skills (HOTS)

Question 1.

Is there any digit whose place value is always equal to its face value irrespective of its position in any number?

Solution:

Yes, the digit is 0.

Question 2.

Write all 4-digit numbers that can be formed with the digits2 and 5, using both digits equal number of time. Also find their sum.

Solution:

Possible numbers are : 2255, 2552, 2525, 5225, 5252, 5522

and their sum = 2255 + 2552 + 2525 + 5225 + 5252 + 5522 = 23331

Thousand Hundred Tens Ones

2 2 5 5

2 5 5 2

2 5 2 5

5 2 2 5

5 2 5 2

5 5 2 2

Question 3.

What is the difference between the smallest 6-digit number with five different digits and the greatest 5-digit number with four different digits?

Solution:

The smallest 6-digit number with five different digits = 100234.

The greatest 5-digit number with four different digits = 99876.

Their difference = 100234 – 99876 = 358

Question 4.

How many times does the digit 3 occur at tert’s place in natural numbers from 100 to 1000?

Solution:

90 times i.e. 3, 13, 23, 33, 43, 53, 63, 73, 83, 93 and upto 983, 993

 

👍👍👍👍👍👍👍👍👍👍👍👍👍👍

ML Aggarwal Class 6 Solutions for ICSE Maths Chapter 1 Knowing Our Numbers 

Question 1.

Write the numeral for each of the following numbers and insert commas correctly:

(i) Six crore nine lakh forty seven.

(ii) One hundred four million seven hundred twenty two thousand three hundred ninety four.

Solution:

(i) 6,09,00,047

(ii) 104,722,394

 

Question 2.

Insert commas suitably and write the numebr 30189301 in words in Indian and International system of numeration.

Solution:

International system : 30,189,301

Three crore one lakh eighty nine thousand three hundred one Thirty million one hundred eighty nine thousand three hundred one

Question 3.

Find the difference between the place value and the face value of the digit 6 in the number 72601.

Solution:

Place value of 6

Question 4.

Write all possible two-digit number using the digits 4 and 0. repetition of digits is allowed.

Solution:

Possible digit numbers = 40, 44

Question 5.

Write all possible natural numbers using the digits 7, 0, 6. Repetition of digits is not allowed.

Solution:

The given digits are 7,0, 6 and repetition of digits is not allowed.

The one- digit numbers that can be formed are 7 and 6.

We are required to write 2-digit numbers.

Out of the given digits, the possible ways of choosing the two digits are

7, 0; 6, 0; 6, 7

Using the digits 7 and 0, the numbers are 70.

Similarily, Using the digits 6 and 0, the numbers are 60

Using the digits 6 and 7, the numbers are 67 and 76.

Hence, all possible 2-digit numbers are

60, 70, 67, 76

Now, We are required to write 3-digit numbers using the digits 7, 0, 6 and the repetition of the digits is not allowed. Keeping 0 at unit’s place, 3-digit number obtained are 670 and 760.

 

Keeping 6 at unit’s place, 3-digit number obtained are 706.

Keeping 7 at unit’s place, 3-digit number obtained are 607.

Hence, all possible 3-digit numbers are : 670, 760, 706 and 607.

All possible numbers using the digits 7, 0 and 6 are

6, 7, 76, 67, 70, 60, 706, 607, 760, 670.

Question 6.

Arrange the following numbers in ascending order:

3706, 58019, 3760, 59801, 560023

Solution:

3706, 3760, 58019, 59801, 560023

Question 7.

Write the greatest six-digit number using four different digits.

Solution:

Greatest six-digits number using four different digit is 999876.

Question 8.

Write the smallest eight-digit number using four different digits.

Solution:

Smallest eight-digit number = 10000023

Question 9.

Find the difference between the greatest and the smallest 4-digit numbers formed by the digits 0, 3, 6, 9.

Solution:

The greatest 4-digit number using 0, 3, 6, 9 = 9630

The smallest 4-digit number using 0, 3, 6, 9 = 3069

∴ Their Difference = 9630 – 3069 = 6561

Question 10.

Find the sum of the four-digit greatest number and the five-digit smallest number, each number having three different digits.

Solution:

Four digit greatest number with three different digits = 9987

Five digit smallest number with three different digit = 10002

∴ Their Sum = 9987 + 10002 = 19989

 

Question 11.

Write the greatest and the smallest four-digit numbers using four different digits with the conditions as given:

(i) Digit 3 always at hundred’s place.

(ii) Digit 0 always at ten’s place.

Solution:

(i) 9387; 1302

(ii)9807; 1203

Question 12.

A mobile number consists of ten digits. First four digits are 9, 9, 7 and 9. Make the smallest mobile number by using only one digit twice from the digits 8, 3, 5, 0, 6.

Solution:

The mobile number is 9979003568.

Question 13.

Two stitch a uniform, 1 m 75 cm cloth is needed. Out of 153 m cloth, how many uniforms can be stitched and how much cloth will remain?

Solution:

Total cloth 153 m = 15300 cm

To stich a uniform, cloth needed

= 1 m 75 cm = 175 cm

Total uniforms can be stiched = 

Hence, 87 uniforms can be stiched 75 cm cloth will remain extra.

class 8 physics heat

 1. Heat is a form of energy. When two bodies are in contact heat flows from body at higher temperature to body at lower temperature till the lower temperature of both is same.

 2. When a body is heated, its molecules move faster about their means position and kinetic energy increases and with fall in temperature their K.E. decreases.

3. When a substance is heated

(i) It expands i.e. a change in size takes place

(ii) Change in temperature takes place.

(iii) Change in state takes place.

4. CHANGE OF STATE : “The process of change from one state to another at a constant temperature is called change of state.”

5. Solid on heating changes into LIQUID. LIQUID on absorbing heat changes to VAPOURS some SOLIDS on heating DIRECTLY change in vapours called SUBLIMATION. Substance is called SUBLIMATE.

SOLIDIFICATION on cooling when a vapours change into SOLID. GAS OR VAPOURS on cooling   changes to LIQUID also called LIQUIFACTION.

6. MELTING: Change of solid into liquid at constant temperature. 

FUSION⇒FREEZING is change of LIQUID into SOLID at constant temperature and change of solid into liquid at a constant _ temperature is called FUSION.

7. EVAPORATION: “Change liquid to gas at ALLTEMPERATURES” It is surface phenomenon. “

8. VAPOURIZATION : “Change of liquid into vapours at fixed temperature”.

 9. METING POINT: “Is the temperature at which a solid starts melting and remains constant till the whole of solid melts.”

M.P. is same as freezing point.

M.P. of ice is 0°C or freezing point, of water is 0°C.

 10. BOILING POINT: “Is the temperature of a liquid at which it start, boiling i.e. change into vapours or gaseous state.”

B .P. of pure water is 100°C.

11. ABSOLUTE ZERO: “The temperature at which molecular motion completely ceases.”

12. FACTORS EFFECTING THE RATE OF EVAPORATION :

(i) Temperature: Increases with increase in temperature

(ii) S.A.: Increases with increase in S.A.

(iii) BLOWING AIR—Renewal of air increases evaporation.

(iv) NATURE—Some liquids like spirit, alcohol, petrol evaporate easily.

 EVAPOURATION → produces coolness, BOILING produces Hotness.

13. LINEAR EXPANSION: When a solid rod (metal) is heated change in length takes place, which depends upon

(i) original length (L0)

(ii) Increase in temperature

(iii) Material of rod.

Let L0 be the original length at 0°C, when heated to T°C final length becomes L

Increase in length (Lt – L0) a L0 (T – 0)

Or

Coefficient of linear expension a which depends upon material of rod.

Lt– L0 = L0 α T

α = Lt – L0 / L0 T = increase in length / original length × Rise in temperature

 When a metal plate is heated, change in area takes place and the expansion is called SUPERFICIAL expansion.

14. When a solid of volume v0 is heated change in volume called cubical expansion takes place.

15. α : β : γ = 1 : 2 : 3

15 Delightful Facts About Dolphins

15 Delightful Facts About Dolphins

1. DOLPHINS ARE EXCELLENT NAPPERS.

Since dolphins can't breathe underwater, they need to swim up to the ocean's surface to get air. So how do they sleep without drowning? Essentially, dolphins are champion power nappers. Rather than sleep for several hours at a time, they rest one hemisphere of their brain for 15 to 20 minutes at a time, and they take these "naps" several times each day. By resting one hemisphere of their brain at a time, dolphins can continue swimming, breathing, and watching for predators 24/7.

2. DOLPHINS COMMUNICATE WITH CLICKS AND WHISTLES …

Dolphins communicate with one another underwater by making a variety of vocalizations. To find prey and navigate the ocean, they make clicking sounds, and they "speak" to other dolphins by whistling. Dolphins also produce loud burst-pulse sounds when they feel excited or aggressive, such as when they need to scare off a nearby shark. Some female dolphins also produce a burst-pulse to reprimand their offspring, called calves, for bad behavior.

3. BUT DOLPHIN LANGUAGE REMAINS A MYSTERY.

Although marine scientists have studied and recorded dolphin vocalizations for decades, many aspects of the animals’ language and how they communicate are still unknown. Scientists have not yet broken down the individual units of dolphin sounds, and they're still searching for a Rosetta Stone that links the animals' vocalizations to their behavior. By using new technologies—including algorithms and high-frequency recorders that work underwater—scientists hope to finally unlock the mystery of the dolphin language.

4. DOLPHINS USE ECHOLOCATION TO NAVIGATE.

To know where they are in relation to other objects and animals, dolphins use echolocation (a.k.a. biological sonar). After emitting a series of high-pitched clicks, they listen for the echoes to bounce off their surroundings. Based on these echoes, dolphins can judge where they are in space and determine the size and shape of nearby objects. Besides helping dolphins evade predators, echolocation allows them to trap, catch, and eat fish and squid.

5. DOLPHINS MAKE FRIENDS WITH OTHER DOLPHINS.

Dolphins are highly social, and scientists are still discovering fascinating details about how the aquatic mammals socialize with one another. In 2015, scientists at Florida Atlantic University's Harbor Branch Oceanographic Institute published research in the Marine Mammal Science journal about the social networks of dolphins. After spending over six years tracking 200 bottlenose dolphins in Florida's Indian River Lagoon, the scientists discovered that dolphins have friends. Instead of spending equal time with the dolphins around them, the animals actually segregate themselves into friend groups. Just like humans, dolphins seem to prefer the company of certain peers more than others.

6. EACH DOLPHIN RESPONDS TO ITS OWN NAME.

Dolphins aren't swimming around with name tags, but every dolphin has its own unique whistle. Scientists believe that dolphins use these signature whistles for life, and female dolphins may even teach their calves their whistles before they're born. Dolphins use their signature whistles to call out to one another and may be able to remember other dolphins' whistles after decades apart.

7. THERE ARE 44 DIFFERENT DOLPHIN SPECIES.

Although bottlenose dolphins are the most well-known and recognizable, there are 43 other dolphin species. Most species live in temperate and tropical oceans, but a few live in colder oceans or rivers. Depending on their species, dolphins can vary considerably in their physical attributes and behavior. For example, the largest dolphin species, the Orca (also called Killer Whale), can be 30 feet long—10 times longer than the smallest dolphins.

8. DOLPHINS DON'T USE THEIR TEETH TO CHEW FOOD.

Dolphins have teeth, but they don't use their chompers to chew food. Instead, dolphins use their teeth to catch prey (fish, crustaceans, and squid) and swallow it whole. Since they forgo chewing, digestion occurs in their stomach—or, more precisely, in part of their stomach. Dolphins have multiple stomach chambers, one of which is devoted to digestion, while the other chambers store food before it's digested.

9. DOLPHINS TYPICALLY GIVE BIRTH TO JUST ONE CALF.

Depending on their species, most female dolphins (called cows) carry their babies for nine to 17 months before giving birth to a calf. Interestingly, calves are born tail first, rather than head first, so they don't drown during the birthing process. After nursing for one to two years, a calf typically stays with its mother for the next one to seven years, before mating and having its own calves.

10. A DOLPHIN'S SKIN CAN BE REGENERATED EVERY TWO HOURS.

If you've ever swum with dolphins, you know their skin looks and feels super smooth and sleek. There's a reason for that—a dolphin's epidermis (outer layer of skin) can be sloughed off and replaced with new skin cells as often as every two hours. Because their skin regenerates so often, it stays smooth and, as most scientists believe, reduces drag as they swim.

11. THE U.S. NAVY TRAINS DOLPHINS TO PROTECT NUCLEAR WEAPONS.

A bottlenose dolphin named K-Dog from the Commander Task Unit jumps out of the water in 2003. Commander Task Unit is comprised of special mine clearing teams from The United Kingdom, Australia, and the U.S.

BRIEN AHO, U.S. NAVY/GETTY IMAGES

Despite dolphins' general friendliness, some of them are trained for combat. The Navy Marine Mammal Program at San Diego's Space and Naval Warfare Systems Command (SPAWAR) trains dozens of bottlenose dolphins (as well as sea lions) to help the U.S. Navy. In the past, the U.S. military has used dolphins in conflicts in Vietnam and the Persian Gulf. Today, thanks to their intelligence, speed, and echolocation skills, dolphins are trained to find enemy swimmers, locate underwater mines, and guard nuclear arsenals.

12. DOLPHINS ARE NOT THE SAME AS PORPOISES.

To the untrained eye, dolphins and porpoises look nearly identical, and many people mistakenly think that porpoises are a type of dolphin. But the two species belong to completely different families and differ in their physical attributes. So how can you tell them apart? Dolphins, which are usually bigger than porpoises, typically have longer beaks and curved dorsal fins. Porpoises, on the other hand, have more triangular dorsal fins as well as spade-shaped (rather than conical) teeth.

13. HUNTING, OVERFISHING, AND RISING OCEAN TEMPERATURES THREATEN DOLPHINS.

Some dolphin species are endangered or functionally extinct (like China's baiji dolphin) due to hunting, overfishing, and pollution. Although dolphin meat is high in mercury, the animals are still hunted for their meat and eaten in parts of Japan and the Faroe Islands of Denm

class 8 electricity

. Write true or false for each statement:

(a) A fuse wire has a high melting point.

Answer. False.

(b) Flow of protons constitutes electric current.

Answer. False.

(c) Silver is an insulator of electricity.

Answer. False.

(d) S.I. unit and commercial unit of electrical energy are same.

Answer. False.

(e) Overloading of electric current in circuits can lead to short circuiting.

Answer. True.

(f) Our body can pass electricity through it.

Answer. True.

(g) All metals are insulators of electricity.

Answer. False.

(h) The earth wire protects us from an electric shock.

Answer. True.

(i) A switch should not be touched with wet hands.

Answer. True.

(j) AH electrical appliances in a household circuit work at the same voltage.

Answer. True.

(k) In a cable, the green wire is the live wire.

Answer. False.

(l) A fuse is connected to the live wire.

Answer. True.

(m) A switch is connected to the neutral wire.

Answer. False.

2. Fill in the blanks

(a) The unit in which we pay the cost of electricity is kWh.

(b) The electrical energy consumed in a house is measured by kWh meter.

(c) In a household electrical circuit, the appliance are connected in parallel with the mains.

(d) A switch is connected to the live wire.

(e) The red colour insulated wire in a cable is the live wire.

(f) One kilowatt hour is equal to 3.6 x 106  joule.

(g) A fuse wire should have low melting point.

3. Match the following

4. Select the correct alternative

(a) All wires used in electric circuits should be covered with

 colouring material

 conducting material

 an insulating material

 none of the above

(b) Electric work done per unit time is

 electrical energy

 electric current

 electric voltage

 electrical power

(c) One kilowatt ¡s equal to

 100 watt

 1000 watt

 10 watt

 none of these

(d) Fuse wire is an alloy of

 tin-lead

 copper-lead

 tin-copper

 lead-silver

(e) A fuse wire should have

 a low melting point

 high melting point

 very high melting point

 none of the above

(f) When switch of an electric appliance is put off, it disconnects

 the live wire

 the neutral wire

 the earth wire

 the live and the neutral wire

(g) The purpose of an electric meter in a house is

 to give the cost of electricity directly

 to give the consumption of electrical energy

 to safeguard the circuit from short circuiting

 to put on or off the mains.

(h) If out of the two lighted bulbs in a room, one bulb suddenly fuses, then

 other bulb will glow more

 other bulb will glow less

 other bulb will also fuse

 other bulb will remain lighted unaffected.

Physics Chapter 8 Electricity

Physics Chapter 8  Electricity

1. ELECTRICITY: “Is the rate of flow of electrons”. i = q/t

2. To keep electrons move, potential difference is needed. This is done by a cell or battery.

3. Potential difference “is the amount of work done in moving a unit positive charge from one point to other.”

Potential difference V = Work done (W) / charge moved (Q)  Or W = QV but charge = it  Hence, W = VIt or Electrical energy = VIt Power is “Rate of doing work” P = W/t = VIt/t = VI

Power is measured in watt or J S-1

4.1 Watt = 1 Volt × 1 Ampere

S.I. unit of charge is coulomb (C).

S.I. unit of current is Ampere (A).

S.I. unit of P.D. is volt.

S.I. unit of electrical energy is Joule (J) and of power is watt (W)

1 kWh-3600000J = 3.6 x 106 J

5. ELECTRIC power is generated at the GENERATING STATION at 11000 volt, or 11 kV as these stations are at very far off place from areas where it is to be used. The voltage (A.C.) is of 50 HZ frequency.

6. AT GRID SUB-STATION this alternating current (A.C) voltage is stepped up from 11 kV to 132 kV to minise the loss of energy in transmission line wires.

7. At MAIN-SUB-STATION this voltage is stepped down from 132 kV to 33 kV and transmitted to city SUB-STATION.

8.  At CITY SUB STATION, it is further stepped down from 33 kV to 220 V for supply to hourses for consumers.

9.  Colour coding: Live wire — Red or Brown

Neutral—Black or light blue

Earth wire — Green or yellow

10.  1 kWh = 1 unit: Power Rating on an appliance 100 W – 220 V means the appliance when worked on a 220 V will consume 100 W electricity power

11. OVER LOADING: is the condition of Electric circuit, when it draws more current than it is designed for i. e. when a number of appliances are switched on at a time i.e. geyser, A.C. Electric motor etc. or a large number of plugs are put in the same socket.

12.  EARTHING: is done in a house near the kWh meter. Earthing is a safety device which puts the appliance at zero potential.

 

13 .SHORT CIRCUITING: If the insulation on the wire of cable used f in the wiring (or used with an appliance) breaks. The LIVE WIRE

COMES IN CONTACT WITH THE NEUTRAL WIRE, this result in SHORT CIRCUITING

14.  FUSE: “Is a device used to limit the current in an electric circuit”. The use of fuse protects the appliance in circuit from being damaged Fuse is always connected in live wire. A fuse wire should have

(i) High resistance

(ii) Low melting point.

These days miniature circuit breakers (MCB) are used. It is AUTOMATIC breaker, when current flowing excess.

15.  Appliances in a house are connected in parallel.

What Causes Turbulence?

No matter how many times you've flown, feeling a plane rattle at 35,000 feet in the air can be an unnerving experience. But turbulence, whether it's a small bump or a stomach-flipping drop, is nothing to get shaken up about. It's a normal part of flying through the ever-shifting atmosphere.

Just like a truck traversing uneven roads or a ship navigating choppy seas, planes often encounter tumultuous, or turbulent, air currents in the skies. These currents can come from several different sources. When flying over high mountains, planes sometimes experience what’s called terrain-induced turbulence. The wind flowing over the peaks and through the valleys disrupts the air thousands of feet above it, resulting in a bumpy ride for any passing aircraft.

Even when flying over flat land, pilots can run into rough patches. Air that's been heated up by the sun at ground level expands and rises to create an updraft. As this updraft travels higher it may cool and condense into a cloud. Cloud-based or convective turbulence is the easiest kind for pilots (and passengers) to spot and prepare for, but not every updraft turns into a menacing cloud. There's also something called clear air turbulence which occurs when the rising hot air is too dry to form into a cloud. Unlike convective turbulence, these problem areas are impossible to identify with the naked eye alone.

So what happens when a plane meets up with one of these drafts in midair? The effects are usually mild: perhaps enough jostling to wake you from your in-flight nap, but not quite enough to topple your drink from its tray. Of course turbulence can become more severe, but in such cases passengers tend to think they're in more danger than they actually are.

"Even in rough turbulence, the plane is never changing altitude more than 10 or 20 feet either way," co-pilot and Cockpit Confidential author Patrick Smith told Mental Floss. "There’s this idea it's plummeting hundreds of feet. Not true."

Planes are built to be tossed and throttled by volatile weather: If you ever see a wing bending like a diving board in high winds, remember it’s supposed to do that. The biggest threat during a bout of turbulence is being knocked around the cabin, which is why most turbulence injuries are sustained by flight attendants. So the next time your pilot announces rough skies ahead, find your seat, fasten your seatbelt, and make note of where the barf bags are.

What exactly are quarks?

Richard Muller:

Quarks are the main components of protons. We have concluded through experimental probing of the proton with high energy electrons that inside the proton there are three massive objects, and based on Murray Gell-Mann’s theory, we call these quarks.

(There are other things inside the nucleus, such as gluons, but they are lighter in weight. The mass is dominated by the quarks.)

The biggest surprise about quarks is that we cannot extract them. If we put enough energy to pull one out, that energy is transformed into the creation of additional quarks, including an antiquark, which binds with the one we extracted, to make (for example) a quark-antiquark pi meson. This feature is a consequence of the fact that the forces between quarks do not decrease with distance. Pi mesons consist of quark-anti-quark pairs.

This property is called confinement, and it means that in the macroscopic world, we will never see a free quark. Quarks can be semi-free in what we call a quark-gluon plasma, but that’s similar to saying that an electron is free when it conducts inside a metal. And unlike the electron, we can’t pull the quark off the surface of the plasma.

There's a First World. There's a Third World. What's the Second World?

We often hear about the plights of the Third World, and most of us have our share of First World problems. But is there something in between—a Second World?

There sure is: the Commies (and now former Commies).

Today, people use the terms First or Third World to rank the development of countries or the strength of their economy. This is a pretty recent development, and veers away from the original usage of the terms, which were coined during the Cold War as part of a rough—and now outdated—model of geopolitical alliances.

The Cold War and the creation of NATO (a military and collective defense alliance formed by the U.S. and its western allies) and the Warsaw Pact (a defense treaty between several communist states in Eastern Europe) roughly divided the major world powers into two spheres with differing political and economic structures—east versus west, communist versus capitalist, the U.S. versus the USSR—with the Iron Curtain in between them.

In 1952, the French demographer Alfred Sauvy coined the term “Third World” to refer to everyone else, the countries unaligned and uninvolved with either side of the Cold War division. With the naming of the Third World, it followed that the Cold War blocs should get numbered, too. The democratic, capitalist countries within the Western sphere of influence became the “First World." The communist-socialist states that were part of or allied with the USSR became the "Second World."

Later, the term "Fourth World" was coined to refer to ethnically or religiously defined populations living within or across national boundaries, nations without a sovereign state, and indigenous groups that are nomadic, uncontacted or living outside of global society.

The Worlds Today

At the end of the Cold War, the three worlds model (not to be confused with Mao Zedong’s differently structured Three Worlds Theory) took on more of an economic context, rather than a geopolitical one. The First World now usually refers to Western, industrialized states, while the Second World consists of the communist and former communist states. The Third World still encompasses “everybody else,” mostly in Africa, Asia, and the Middle East, and tends to be a catchall for “developing nations” that are poor, less technologically advanced, dependent on the “developed countries,” or have unstable governments, high rates of population growth, illiteracy and disease, a lack of a middle class, a lot of foreign debt, or some combination thereof.

What are antibiotics made of?

What are antibiotics made of?

Drew Smith:

Most antibiotics are based on natural products synthesized by bacteria and fungi. Quinolones (like Cipro) and sulfa drugs (like sulfamethoxazole) are the major exceptions to this rule.

Antibiotics belong to a class of natural compounds called secondary metabolites. These are molecules that are not essential to normal growth and metabolism (like sugars, amino acids, and nucleic acids) but perform specialized roles. Secondary metabolites enable creatures that can’t move or speak to communicate, control their environments and defend themselves.

Bacteria, plants, and fungi are much better than human chemists at creating complex molecules. These biosyntheses are often accomplished in factories within cells, large complexes of enzymes in which various precursors and intermediates are assembled, modified, and passed on.

Although total synthesis of vancomycin has been accomplished in labs, I believe that it is still produced commercially by fermentation of the bacterium Amycolatopsis orientalis from which it was first isolated.

The thing to keep in mind about these secondary metabolites is that anything that is made by an enzyme can also be broken down by an enzyme—often the same one that made it. Small tweaks to these enzymes, or just putting them in a different environment, can cause them to degrade antibiotics. Antibiotic resistance is thus an intrinsic and inevitable feature of antibiotic use.

The world’s 15 largest national parks

What’s the biggest national park in the world? Great question, and one that’s not actually very easy to answer. The issue comes with the definition of what a national park actually is, a topic we explain in some detail further down the page.

The below list of the world’s largest national parks covers all areas of protected, recreationally accessible land in the world – including marine reserves, transnational parks (where bordering national parks from two or more countries have combined into one protected area), and ‘national monuments’ in the US (areas similar to national parks, but created from land controlled by the federal government and by proclamation of the president).

So, without further ado – but with the above caveats in mind – here are out candidates for the largest national parks in the world:

The world’s 15 largest national parks

1. Papahānaumokuākea Marine National Monument, US (Hawaii): 1,510,000 km sq

The largest national park in the world is Papahānaumokuākea Marine National Monument. It was established by Presidential Proclamation in 2006 and encompasses over 1.5 million square kilometers of the Pacific Ocean – an area larger than all the national parks of the United States combined.

The name Papahānaumokuākea commemorates the union of Papahānaumoku and Wākea, two honoured Hawaiian ancestors. The area is considered sacred by native Hawaiians – a place from which all life springs, and where spirits return to after death.

With 2,200 km of coast around coral islands, shoals, and banks, the area hosts a staggering diversity of coral, fish, birds, marine mammals, many endemic to the Hawaiian archipelago.

2. Northeast Greenland National Park, Greenland: 972,000 km sq

The Northeast Greenland National Park was created in 1974, then expanded in 1988 to its present size, making it the largest land national park in the world. If Northeast Greenland National Park were a country it would be the 31^st largest country in the world – in between Egypt and Tanzania.

Wildlife in the park includes plenty of mammals, including around 40% of the world’s total population of musk oxen. In addition, there are arctic fox, stoat, collared lemming, and arctic hare, with many polar bears and walrus found around the coastal regions, and a wide variety of seal and whale species in the surrounding waters.

3. The Kavango Zambezi Transfrontier Conservation Area, Zambia, Botswana, Namibia, Zimbabwe, and Angola: 519,912 km sq

Coming in at twice the size of the United Kingdom, the Kavango Zambezi Transfrontier Conservation Area lies in the river basins of the Kavango and Zambezi, and stretches across five Southern African countries – Angola, Botswana, Namibia, Zambia, and Zimbabwe.

Highlights of the park include the Okavango Delta (the world’s largest inland delta) and the awe-inspiring Victoria Falls, though the whole park is richly endowed with a diversity of wildlife-dense ecosystems that make it one of the best places in the world for enjoying a safari.

4. Phoenix Islands Protected Area, Republic of Kiribati: 408,250km sq

The Phoenix Island Protected Area (PIPA) is a huge expanse of marine and land ecosystems in the Southern Pacific Ocean, surrounding the Kiribati group of islands known as Phoenix Island Group. The isolation of the area means that PIPA is a crucial habitat for migratory species as they traverse the Pacific Ocean, and as such is on the UNESCO World Heritage List

Alongside 14 seamounts presumed to be underwater extinct volcanoes, PIPA has approximately 800 known animal species, including around 200 coral species, 500 fish species, 18 marine mammals, and 44 species of birds.

 5. Great Barrier Reef Marine Park, Australia: 344,400 km sq

Located off the coast of Queensland in North-Eastern Australia, the Great Barrier Reef is the world’s largest coral reef system – made up of  900 islands and almost 3,000 individual reefs stretching for over 2,00 kilometers. The reef is so large and looks so distinct from the air that it can be seen from space.

The size and location of the reef make it home to an incredible array of sea life – over 1,500 fish species, 125 species of sharks and rays, 30 whale species, 17 species of sea snake, six turtle species and a large dugong population, as well as plenty of giant saltwater crocodiles. More than 5,000 molluscs have been recorded, along with 400 species of hard and soft coral. It’s due to this biodiversity that the Great Barrier Reef is a World Heritage Site, and one of the seven natural wonders of the world.

6. Galapagos Marine Reserve, Ecuador: 133,000 km sq

Aside from being one of the world’s largest marine reserves, thanks to its position on the equator the Galapagos Marine Reserve is also one of the most biologically diverse marine areas in the world. The reserve lies 1,100 kilometers off the coast of Ecuador and covers 133,000 square kilometers of Pacific Ocean around the Galapagos Islands.

The reserve is made up of several different terrains including underwater volcanoes, mountains, cliffs and coral below sea level, and wetlands and lagoons at sea level. These ecosystems are home to over 2,900 recorded animal species, including whales, dolphins, albatrosses, sharks, sea lions, penguins, fur seals, rays, cormorants, marine iguanas, sea turtles, and tropical fish.

7. The Great Limpopo Transfrontier Park, South Africa, Mozambique & Zimbabwe: 99,800 km sq

The Great Limpopo Transfrontier Park (GLTP) links together a number of national parks that border the countries of South Africa (Kruger National Park), Mozambique (Limpopo National Park), Zimbabwe (Gonarezhou National Park, Manjinji Pan Sanctuary and Malipati Safari Area).

GLTP comprises a huge area of the lowland savannah bisected by the Lebombo Mountains and includes five major river systems. All of this terrain is home to an incredible 500 bird species, as well as at least 147 mammals, 116 reptiles, 49 species of fish and 34 species of frogs, and makes for one of the world’s premier safari destinations.

8. Arctic National Wildlife Refuge, US (Alaska): 78,051 km sq

The Arctic National Wildlife Refuge (ANWR) in north-eastern Alaska came into being in 1980 and is the largest national wildlife refuge in the US. The refuge supports the most diverse collection of animal and plant life found in the Arctic Circle, where the northern coast consists of the barrier islands, river deltas, coastal lagoons, and salt marshes, all providing habitats for migratory waterbirds and shorebirds.

The interior of the reserve is home to herds of caribou, muskoxen, and migratory birds – including flocks of tens of thousands of snow geese which stopover during September to feed, before migrating south. US Congress recently voted to open ANWR to oil drilling, meaning its future is currently uncertain.

9. Yukon Delta National Wildlife Refuge, Canada: 77,538 km sq

The Yukon Delta National Wildlife Refuge in southwestern Alaska is a coastal plain covering the delta of Alaska’s two largest rivers – the Yukon and Kuskokwim – and extending to the Bering Sea, incorporating some nearby volcanic islands.

The refuge is rich in wildlife and supports one of the largest concentrations of waterbirds in the world. The narrow strip of coast is the most productive goose nesting habitat in Alaska, while the drier uplands are inhabited by brown and black bears, caribou, moose, wolves, coyote, lynx and musk oxen. The refuge is also home to around 25,000 Yup’ik Eskimos living in village settlements on a subsistence lifestyle.

10. Queen Maud Gulf Migratory Bird Sanctuary, Canada: 61,765 km sq

The Queen Maud Gulf Migratory Bird Sanctuary is the largest protected area in Canada, established in 1961 to protect the largest variety of geese found in any North American nesting area.

Since its inception – and because of its size – the sanctuary has become an important area for the many other species of migratory birds and wildlife it supports. This includes over 2 million white geese (over 90% of the world’s Ross’s goose and 8% of the Canadian snow goose), tundra swan, brand, and many species of waterfowl, shorebirds and land birds.

11. Selous Game Reserve, Tanzania: 54,600 km sq

Named after the great explorer and hunter Frederick Courtney Selous, the Selous Game Reserve is located in southern Tanzania and is Africa’s largest game reserve –three times the size of South Africa’s Kruger National Park, and twice the size of the Serengeti National Park.

The reserve is relatively unimpacted by human activity and was designated a UNESCO World Heritage Site in 1982 due to the diversity of the wildlife. This includes one of the most significant concentrations of elephant and black rhinoceros in Africa, alongside high numbers of cheetah, giraffe, crocodile, and hippo.

12. Wrangell-St Elias National Park & Preserve, US (Alaska): 53,321 km sq

Wrangell St. Elias National Park is the largest National Park in the United States – around six times the size of Yellowstone National Park – and rises from sea level up to 18,008 feet at the peak of Mount St Elias, second highest mountain in the US.

Four major mountain ranges converge in Wrangell, meaning a wide variety of natural features including mountain peaks, glaciers, volcanoes, rivers, and boreal forests. Roughly 70% of the park is designated and managed as wilderness.

13. Central Kalahari Game Reserve, Botswana: 52,000 km sq

The Central Kalahari Game Reserve (CKGR) is an unforgiving, harsh terrain covering a large swathe of central Botswana. It’s still relatively inaccessible and remote, with very little human impact – only a handful of visitors each year. Whilst it’s essentially a desert, there are grasslands that make it home to wildlife species including giraffes, cheetahs, wild dogs and hyenas, and wild dogs. For a remote safari where you’re all but guaranteed to be on your own with the wildlife, CKGR is pretty hard to beat!

14. Namib-Naukluft National Park, Namibia: 49,768 km sq

Namibia’s largest national park at a whopping 49,000km sq, the Namib Naukluft National Parl in the Namib Naukluft desert is one of the most intensely studied – and oldest – deserts on earth. Made up of mountains, sand seas, moonscapes, and riverbeds, each morning and evening the sun paints the never-ending dunes around Sossusvlei in dramatic hues and shadows – a sight not to be missed.

Most of the park is uninhabited, but there has been a human presence since early Stone Age man passed through, leaving behind stone hand axes. These days the park provides very occasional hunting grounds for the San, and a permanent base for the 300 or so Topnaar people in 13 small villages along the lower Kuideb River.

15. Wood Buffalo National Park, Canada: 44,807 km sq

Last but not list in this list of world’s largest national parks is Wood Buffalo National Park – Canada’s largest national park, established in 1922 to protect the last free-roaming herds of wood bison. In 1983 is was designated a UNESCO World Heritage Site for the biological diversity of the Peace-Athabasca Delta – one of the largest freshwater deltas in the world – including one of the only known natural nesting sites of the whooping crane.

Other wildlife in the park include wolves, moose, black bears, and beavers.