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Mathematics Pratomsuksa 5 Chapter 1 Notes

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Rounding off whole numbers

Example: Round off 27, 684 to the nearest (a) ten (b) thousand

(a)hundreds

thousandsten thousands

ones(containsdigit to beconsidered)

tens(contains digit to be rounded)

4 is less than 5, so retain 8 and replace the digit to the right of 8,that is 4, with zero.

So, 27, 684 rounded off tothe nearest ten

27, 680

(b)thousands

(contains digitto be rounded)

hundreds(contains digit tobe considered)

6 is more than 5, so add 1 to 7 to get 8 and replace all digits to theright of 7, that is 6, 8 and 4, with zeros.

So, 27, 684rounded off to

the nearest thousand 28, 000

1 W h o l e N u m b e r s

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Mathematics Pratomsuksa 5 Chapter 1 Exercises

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A

Round off each of the following numbers to the nearestten.

Number Nearest ten Number Nearest ten

82 80 78 80

515 520 823 820

3,429 3,430 6,778 6,780

13,211 13,210 92,688 92,690

333,216 333,220 762,575 762,580

8,926,177 8,926,180 25,626,313 25,626,310

B Round off the following to the nearest ten.

1. The length of Rama VIII Bridge is 475 meters.

The length of Rama VIII Bridge is about 480 meters.

2. There are 15,242 bottles of mineral water in the warehouse.

There are about 15,240 bottles of mineral water in thewarehouse.

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Mathematics Pratomsuksa 5 Chapter 1 Exercises

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C Round off the following numbers to the nearest hundred.

Number Nearest

hundred

Number Nearest

hundred

342 300 769 800

2,629 2,600 6,134 6,100

72,163 72,200 48,729 48,700

342,228 342,200 642,550 642,600

2,142,652 2,142,700 411,217,990 411,218,000

12,547,103 12,547,100 72,894,383 72,894,400

D Round off the following to the nearest hundred.

1. The distance from Bangkok to Phuket is 862 km.

The distance from Bangkok to Phuket is about 900 km.

2. A market trader sold 102,729 boxes of apples a year.

A market trader sold about 102,700 boxes of apples a year.

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Mathematics Pratomsuksa 5 Chapter 1 Exercises

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E Round off the following numbers to the nearest thousand.

Number Nearest

thousand

Number Nearest

thousand

2,429 2,000 8,788 9,000

35,501 36,000 64,399 64,000

736,600 737,000 341,499 341,000

3,627,349 3,627,000 9,129,729 9,130,000

24,837,519 24,838,000 63,749,393 63,749,000

56,499,666 56,500,000 32,200,991 32,201,000

F Round off the following to the nearest thousand.

1. The population of Bangkok is 8,160,522.

The population of Bangkok is about 8,161,000 .

2. Shop Y sold 8,409,399 exercise books.

Shop Y sold about 8,409,000 exercise books.

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Mathematics Pratomsuksa 5 Chapter 1 Exercises

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G Round off each of the following numbers to the nearest ten,hundred and thousand.

Number Nearest ten Nearesthundred Nearestthousand

2,436 2,440 2,400 2,000

8,753 8,750 8,800 9,000

32,429 32,430 32,400 32,000

46,796 46,800 46,800 47,000

399,652 399,650 399,700 400,000

696,711 696,710 696,700 697,000

2,714,388 2,714,390 2,714,400 2,714,000

6,216,395 6,216,400 6,216,400 6,216,000

73,549,376 73,549,380 73,549,400 73,549,000

56,699,560 56,699,560 56,699,600 56,700,000

35,516,357 35,516,360 35,516,400 35,516,000

89,124,999 89,125,000 89,125,000 89,125,000

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Mathematics Pratomsuksa 5 Chapter 1 Mastery Practice

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1. Round off 3,219 to the nearestten.A 3,210 C 3,200B 3,220 D 3,000

2. Round off 37,525 to the nearesthundred.A 40,000 C 37,500B 38,000 D 37,530

3. Round off 728,364 to thenearest thousand.A 730,000 C 728,400B 728,000 D 728,360

4. Which of the followingnumbers becomes 27,000when rounded off to thenearest thousand?

A 26,480 C 27,480B 26,380 D 27,580

5. Which of the followingnumbers becomes 95,390when rounded off to thenearest ten?A 95,382 C 95,392B 95,370 D 95,399

6. Which of the followingnumbers becomes 140,000when rounded off to thenearest hundred?A 139,260 C 139,921B 139,961 D 140,100

7. A company made a profit ofB239,625 in one year. What isthis figure to the nearest ten?

A B239,630

B B239,600

C B240,000

D B200,000

8. The number of people anaeroplane can carry is 328.

What is this figure to thenearest ten?A 320B 330C 400D 500

9. The exact number of ticketssold was 13,872. This number

was reported in the newspaperto the nearest hundred. Whatwas that figure?A 13,872B 13,870C 13,900D 14,000

10. The distance betweenBangkok and Hawaii is 12,739km. What is this distance whenrounded off to the nearestthousand?A 13,000B 12,700C 12,600D 12,000

M a s t e e r y P r a c t i c M a s t e e r y P r a c t i c