How_To_Be_Good_At_Math

122 CALCULATING •^ MORE LONG MULTIPLICATION

More long

multiplication

When we need to multiply a number that has more than two digits by a

two-digit number, we can also use long multiplication. It may look trickier

with such a large number, but all we need to do is use more steps.

Let’s multiply 7242 by 23.

Start by writing the two numbers out

like this, with digits that have the same

place values lined up one above the other.

Now we're going to multiply each of the

digits on the top row by each of the digits

on the bottom row, starting with the ones.

First, multiply the 2 ones by 3 ones.

The answer is 6 ones. On a new line,

write 6 in the ones column.

Now multiply 2 hundreds by 3 ones.

The answer is 6 hundreds. Add the

1 hundred that we carried over from the

tens multiplication to make 7 hundreds.

Write the 7 in the hundreds column.

We’re going to

multiply each

digit on the top

row by 3 ones

7242 × 23 =?

7242

23

H T O

×

ThTThHTh

7242

23

H T O

×

ThTThHTh

6

Next, multiply 4 tens by 3 ones.

The answer is 12 tens, or 120.

Write 2 in the tens column. The 1 stands

for 1 hundred, so we carry it over into

the hundreds column to add on at

the next stage.

ThTThHTh H T O

7242

23

26

×

Multiply

2 ones by

3 ones

Multiply

4 tens by

3 ones

ThTThHTh H T O

7242

23

726

×

Multiply

2 hundreds

by 3 ones

1

1

The 1 carried

over is added

to the number

put in this

column

1 carried into

the hundreds

column

122-123_More_long_multiplication.indd 122 29/02/2016 14:11