How_To_Be_Good_At_Math

NUMBERS • FACTORS 29

Next, we test whether 2 is a factor and

find that 2 × 15 = 30. So, 2 and 15 are

factors of 30. We put 2 just after 1 and 15

at the other end, just before 30.

To find all the factors of 30, first write 1

at the beginning of a line and 30 at the

other end, because we know that every

number has 1 and itself as factors.

Next, we check 3 and find that 3 × 10 = 30.

So, we can add 3 and 10 to our row of

factors, the 3 after 2 and the 10 before 15.

When we check 4, we can’t multiply it by

another whole number to make 30. So, 4

isn’t a factor of 30. It doesn’t go on our line.

We check 5 and find that 5 × 6 = 30. So we

add 5 after 3, and 6 before 10. We don’t

need to check 6 because it’s already on our list.

So, our row of factors of 30 is complete.

Common factors

When two or more numbers have the same factors, we call them common factors.

Finding all the factors

If you need to find all the factors of a number, here’s a way to

write down your findings to make sure you don’t miss any out.

24

(^12)
3
4
8
32
1 2
4
(^168)
32
The highest
common
factor is 8
1 × 30 = 30
2 × 15 = 30
3 × 10 = 30
4 ×? = 30
5 × 6 = 30
1 2 3 5 6 10 15 30
1 2 3 10 15 30
1 2 3 10 15 30
1 2 15 30
1 30
24
6
12
FACTORS OF 24 FACTORS OF 32
Here are the factors of 24 and 32. Both
have factors of 1, 2, 4, and 8. These are
their common factors, in yellow circles.
The largest of the common factors is 8.
We call it the highest common factor,
sometimes shortened to HCF.
028_029_Factors_WhatisFactor.indd 29 29/02/2016 18:56