How_To_Be_Good_At_Math

NUMBERS • SUBTRACTING DECIMALS 63

Subtracting decimals

When we subtract decimal numbers, we use the same method

as we do for whole numbers.

First, let’s subtract 0.7,

the decimal part of

4.7, from 8.2. We exchange

a ones strip for ten tenth

cubes so we can take

away seven tenths. The

answer is 7.5.

Let’s try the calculation

8.2 − 4.7. We’ll use the

counting cubes to help us

see what happens.

Now let’s subtract 4,

the whole number,

from 7.5. When we remove

four of the ones strips, we

have 3.5 left.

So 8.2 − 4.7 = 3.5.

We can write the

calculation in columns, like

this. Find out more about

column subtraction on

pages 96-97.

−

After we remove seven

tenths, we have seven

ones and five tenths left

Now we take away

four ones from our

number, 7.5

There are three ones

and five tenths left

One of the ones block is exchanged for ten tenths

Eight ones and two tenths make 8.2 We are taking away four

ones and seven tenths from

our original number, 8.2

TRY IT OUT

Over to you!

Find out how much you’ve learned

by trying out these calculations.

Answers on page 319

10.2 + 21.6 =? 96.7 − 75.8 =?

0.2 + 3.9 =? 45.6 − 21.2 =?

0.5 + 0.7 = 1.2

so 8.2 − 4.7 = 3.5

− = or 8.2 − 0.7 = 7.5

− = or 7.5 − 4 = 3.5

− =? or 8.2 − 4.7 =?

8.2 4.7

8.2 0.7 7.5

7.5 4 3.5

8.2

3.5

7

O 101

4.7

1

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