STRAND: Number
TOPIC:
Multiples, factors & primes
Factor pairs
A number that divides exactly into another number is a factor of that number. The result of the division (that is, the quotient) is
also a factor. These two factors form a factor pair. For example, if 7 is a factor of 35, then 5 is also a factor of 35, since 35 ÷ 7
= 5 and so 5 and 7 form a pair of factors of 35.
The product of the numbers in a factor pair is always equal to the number whose factors they are. For example, if 3 and 6 is
a factor pair of 18, then 3 × 6 = 18.
WORKED Example
Find the missing factor in each of the following factor pairs of 12:
2 and __ , 4 and __ .
THINK
1
2
To find the missing factor, divide 12 by the
known factor of the pair.
Repeat step 1 for the second pair.
WRITE
12 ÷ 2 = 6
So a factor pair of 12 is 2 and 6.
12 ÷ 4 = 3
So a factor pair of 12 is 4 and 3.
Note: There is an alternative way of finding a missing factor. For example, if 2 is a factor of 12, we can obtain the other factor
by finding the number that will give 12 when multiplied by 2. That is, since 2 × 6 = 12, 2 and 6 form a pair of factors of 12.
Try these
1 Find the missing factor in each of the following pairs of factors of 24:
3 and __ , 6 and __ , 12 and __ .
2 Find the missing factor in each of the following pairs of factors of 39:
3 and __ , 39 and __ .
3 Find the missing factor in each of the following pairs of factors of 60:
4 and __ , 5 and __ , 10 and __ , 20 and __ , 30 and __ .
4 Find the missing factor in each of the following pairs of factors of 48:
1 and __ , 4 and __ , 6 and __ , 16 and __ , 24 and __ .
 John Wiley & Sons Australia, Ltd 2001