Page 39 - Cambridge Checkpoint Mathematics Coursebook 7_Slide 02

3.4 Rounding

3.4 Rounding

Sometimes you need to round numbers. When you round a number you get an approximate value.
To round a number:
• to the nearest 10, look at the digit in the units column If the value of the digit is 5 or
• to the nearest 100, look at the digit in the tens column more, round up. If the value is
• to the nearest 1000, look at the digit in the hundreds column. less than 5, round down.

Worked example 3.4A

Round 12 874 to the nearest: a 10 b 100 c 1000.

a 12 874 = 12 870 (to the nearest 10) The digit in the units column is 4. As 4 is less than 5, round
down. The 7 in the tens column stays the same.

b 12 874 = 12 900 (to the nearest 100) The digit in the tens column is 7. As 7 is more than 5, round
up. The 8 in the hundreds column is replaced by 9.

c 12 874 = 13 000 (to the nearest 1000) The digit in the hundreds column is 8. As 8 is more than 5,
round up. The 2 in the thousands column is replaced by 3.

To round a decimal number: • to the nearest whole number, look at the digit in the tenths column
• to one decimal place, look at the digit in the hundredths column.

Worked example 3.4B
Round 13.524 cm: a to the nearest whole number b to one decimal place.

a 13.524 cm = 14 cm The digit in the tenths column is 5 so round up.
(to the nearest whole number) The 3 in the units column becomes a 4.

b 13.524 cm = 13.5 cm The digit in the hundredths column is 2. As 2 is less
(to one decimal place) than 5, round down. The 5 in the tenths column
stays the same.

F Exercise 3.4

1 Round each number to the nearest 10.
a 32 b 78 c 145 d 363 e 1479 f 3804
2 Round each number to the nearest 1000.
a 1200 b 2550 c 3707 d 8090 e 13892 f 792

3 Razi says: ‘If I round 496 to the nearest 10 and to the nearest 100, I get the same answer!’
Is Razi correct? Explain your answer.

4 Round each number to one decimal place.
a 0.63 b 8.27 c 2.461 d 9.194 e 12.861 f 0.066
5 Kylie and Jason are both rounding 23.981 to one decimal place.
Kylie gets an answer of 24 and Jason gets an answer of 24.0.
Who is correct? Explain your answer.
3 Place value, ordering and rounding 37