How_To_Be_Good_At_Math

134 CALCULATING •^ DIVIDING WITH FACTOR PAIRS

Dividing with factor pairs

You’ll remember that a factor pair is two numbers that we multiply together

to get another number (see pages 28 and 101). Factor pairs are just as

useful in division as they are in multiplication.

4

30 2

60

1 × 12 = 12

2 × 6 = 12

3 × 4 = 12

4 × 3 = 12

6 × 2 = 12

12 × 1 = 12

FACTOR PAIRS OF 12 DIVISION FACTS OF 12

12 ÷ 12 = 1

150 ÷ 50 =?

150 ÷ 50 = 3

If we divide 12 by one of the numbers from a

factor pair, then the answer will be the other

number in the pair. For example, 12 ÷ 3 must be 4,

because 3 and 4 are a factor pair of 12.

These are all the factor pairs of 12. The

inverse of each multiplication fact is a

division fact of 12. The multiplier of the factor

pair becomes the divisor in the division fact.

Factor pairs and multiples of 10

You can also use factor pairs when you are dividing with numbers

that are multiples of 10. The only thing that’s different is the zeros

• all the other digits are the same. Here are some examples.

The multiplier of

each factor pair

is now the divisor

This is also true of other multiples

of 10. For example, 5 and 3 are a

factor pair of 15, because 5 × 3 = 15.

So the answer to 150 ÷ 50 must be 3.

120 ÷ 60 =?

120 ÷ 60 = 2

What about 120 ÷ 60? Since

6 and 2 are a factor pair of

12, 60 and 2 must be a factor pair

of 120. So the answer is 2.

120 ÷ 30 =?

120 ÷ 30 = 4

Let’s look at 120 ÷ 30. The answer

is 4. You know that 3 and 4 are a

factor pair of 12, so 30 and 4 must

be a factor pair of 120.

This is the

multiplier

12 ÷ 6 = 2

12 ÷ 4 = 3

12 ÷ 3 = 4

12 ÷ 2 = 6

12 ÷ 1 = 12

134-135_Dividing_with_factor_pairs.indd 134 29/02/2016 14:11