How_To_Be_Good_At_Math

94 CALCULATING •^ EXPANDED COLUMN SUBTRACTION

Expanded

Column subtraction...............

To find the difference between numbers with more than two digits, we

can use column subtraction. The method shown here, called expanded

column subtraction, is useful if you find the ordinary column subtraction

(shown on pages 96-97) difficult.

−

324

1 78

Next, we add tens. Adding 20

to 180 makes 200, the nearest

multiple of 100. Write the 2 in the tens

column and the 0 in the ones column.

Write the new total on the right.

Let’s think of the calculation 324 − 178 as

finding the difference between 324 and 178.

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’re going to add numbers

that are easy to work with to 178 until

we get to 324.

First, we add on ones that will take

178 up to the nearest multiple of

ten. Adding 2 to 178 makes 180. Write 2

in the ones column. Keep track of the

total, by writing 180 on the right.

Write the

numbers so

that digits with

the same place

value are lined

up like this

H T O

−

324

1 78

H T O

We are going to

add numbers on

to 178 until we

reach 324

−

324

178

H T O

2 180

This is where we

keep track of the

total so far

−

324

1 78

H T O

2 180

Adding 20 to

180 takes the

total up to 200

20200

324 − 178 =?

094_095_Expanded_column_subtraction.indd 94 29/02/2016 14:10