Page 15 - 新思维数学学生用书6 样章

1 The number system

1.2 Rounding decimal numbers

We are going to …

• round a number with 2 decimal places to the nearest whole number

• round a number with 2 decimal places to the nearest tenth.

Rounding makes it easier to describe and

understand numbers. It is easier to nearest
understand that an athlete ran 100 metres round

in less than 10 seconds than the athlete

ran 100 metres in 9.63 seconds.

Worked example 2

Round these numbers to the nearest tenth.

a 8.80 b 6.45 c 3.95

a 8.8 b 6.5 c 4.0 If the hundredths digit is 0, 1, 2, 3 or 4, round

down by keeping the tenths digit the same.
If the hundredths digit is 5, 6, 7, 8 or 9, round up

by increasing the value of the tenths digit by 1.

If the tenths digit is 9, it will change to 0 and the
ones digit will increase by 1.

There must always be 1 decimal place in the

answer, even if it is zero.

Exercise 1.2

1 Round these decimals to the nearest whole number.

4.09 7.89 2.55 7.45

2 Leo bought a book costing $14.65.
What is the cost of the book to the nearest dollar?

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