How_To_Be_Good_At_Math

120 CALCULATING •^ LONG MULTIPLICATION

Long multiplication

Now we’re going to look at another method of long

multiplication (which we also looked at on pages 118-19).

It’s another way to multiply numbers that have two or more

digits, but this method is quicker.

Next, multiply 8 tens by 3 ones.

The answer is 24 tens. Add the 1 ten

that we carried over from the ones

multiplication to make 25 tens, or 250.

Write the 2 in the hundreds column and

the 5 in the tens column.

86

86

86

43

43

43

258

8

Once you understand how

to do long multiplication,

you can use it for

multiplying two numbers

with any number of digits.

Let’s multiply 86 by 43 using

long multiplication.

Start by writing the two numbers out

like this, with digits that have the

same place values 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 multiply each of

the digits on the top row by each of

the digits on the bottom row. Start by

multiplying all the numbers on the top

row by 3 ones.

First, multiply 6 ones by 3 ones.

The answer is 18 ones. On a new line,

write 8 in the ones column. The 1 stands

for 1 ten, so we carry it over into the tens

column to add on at the next stage.

86

43

Write the

numbers so

that the digits

with the same

place value are

lined up like this

We’re going

to multiply

each digit on

the top row

by 3 ones

Multiply

6 ones by

3 ones

1 ten carried

into the tens

column

The 1 ten carried

over is added to

the number put

in this column

1

1

Th H T O

Th H T O

Th H T O

Th H T O

×

×

×

×

86 × 43 =?

Multiply

8 tens by

3 ones

120_121_Long_multiplication.indd 120 29/02/2016 14:11