How_To_Be_Good_At_Math

NUMBERS • ROUNDING DECIMALS 61

Rounding to one

This means that we round

a decimal to the nearest whole

number. So 1.3 is rounded down

to 1 and 1.7 is rounded up to 2.

Rounding to tenths

This means that we round

a decimal number to one digit

after the decimal point. So

1.12 rounds down to 1.1, and

1.15 rounds up to 1.2.

Rounding to hundredths

Rounding to hundredths

gives us a number with two

digits after the decimal point.

So 1.114 rounds down to 1.11

and 1.116 rounds up to 1.12.

Decimals workout

Here’s a list of the racers’ times for the slalom skiing

race on Megabyte Mountain. Can you round all their

times to hundredths, so there are two digits after the

decimal point? Who had the fastest time?

TRY IT OUT

Answer on page 319

Rounding decimals

We round decimals in the same way as we round whole

numbers (see pages 26-27). The easiest way to see how it

works is by looking at a number line.

1 1.3 1.7 2

1.3 is nearer to 1 than 2,

so we round it down

1.114 rounds down

to 1.11

1.116 rounds up

to 1.12

Digits 4 or less are

rounded down

1.7 is nearer to 2 than

1, so it’s rounded up

1.1 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.2

Digits 5 or more

are rounded up

1.11 1.111 1.112 1.113 1.114 1.115 1.116 1.117 1.118 1.119 1.12

The rounding rule for decimals

and whole numbers is the

same: digits less than 5 are

rounded down, and digits of

5 or more are rounded up.

FINISH

TWERG

BLOOP

GLOOK

KWONK

ZARG

17.239 SEC

16.560 SEC

17.211 SEC

16.129 SEC

16.011 SEC

060-061_Comparing_Ordering_Decimals.indd 61 29/02/2016 14:09