How_To_Be_Good_At_Math

96 CALCULATING •^ COLUMN SUBTRACTION

Column subtraction

Using column subtraction is an even quicker way of subtracting large

numbers than expanded column subtraction (see pages 94-95). It

looks tricky to subtract as we go, but we can exchange numbers with

other columns to help us.

Change the 3 in the tens column

into a 2 to show that we have

exchanged a ten.

−

932 − 767 =?

Let’s subtract 767 from 932 using

column subtraction.

Start by writing the two numbers out

like this, with digits that have the

same place value lined up one above the

other. It might help you to label the place

values, but you don’t have to.

Now we are going to subtract each

of the digits on the bottom row from

the digit above it on the top row, starting

with the ones.

We can't subtract 7 ones from 2 ones

here, so let’s exchange 1 ten from the

tens column for 10 ones. Write a little 1

next to the 2 in the ones column to show

that we now have 12 ones.

First we're going

to subtract the

ones

Change this from

3 tens to 2 tens

because we exchanged

1 ten for 10 ones

H T O

767

932

Write the

numbers so that

the digits with

the same place

value are lined

up like this

−

H T O

932

−

H T O

1

−

H T O

767

We can't subtract

7 ones from 2 ones,

so we exchange 1 ten

for 10 ones

12

767

932

767

932

096_097_Column_subtraction.indd 96 29/02/2016 14:10