How_To_Be_Good_At_Math

26 NUMBERS •^ ROUNDING

Rounding

Rounding means changing a number to another

number that is close to it in value, but is easier to

work with or remember.

Rounding up and rounding down

The rounding rule is that for

digits less than 5, we round

down. For digits of 5 or

more, we round up.

2120 22 23 24 25 26 27 28 29 30

Look at 24

on this number

line. It’s closer to

20 than to 30, so we

round it down to 20.

Now let’s look at

28. It’s nearer to
    30 than 20, so we
    round it up to 30.

What about 25?

It’s exactly halfway

between 20 and 30.

The rounding rule is

to round it up to 30.

Rounding to the

nearest hundred

To round to the nearest 100,

we look at the tens digit and

follow the rounding rule.

Let’s round 337 and 572.

Rounding to

the nearest ten

We use the ones digit to

decide whether to round

up or down to the nearest

ten. Let’s round 83 and 89.

80 83 85 89 90

572

We round

numbers “up” or

“down”, depending

on where they are on

the number line.

Rounding using place value

When we round numbers, we use the

place values of a number’s digits.

Digits less than 5

are rounded down

Digits 5 or more are

rounded up

300 337 400 500 600

The ones digit is

3, so we round

down to 80

The ones digit is

9, so we round

up to 90

The tens digit is 3,

so we round down

to 300

The tens digit is

7, so we round

up to 600

026_027_Rounding_Numbers.indd 26 29/02/2016 14:08