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Finding Factors

(KS2, Year 4)

Finding Factors

The factors of a number can be found.

A Simple Example of How to Find Factors

Finding the factors of a number is easy. Find pairs of numbers that multiply to make that number.

Question

What are the factors of the number 18?

Step-by-Step:

1

1 and the number itself (18) are factors of 18.
1 × 18 = 18
Write 1 and 18 on the outside of a grid. 1 and 18 on the outside of a grid

2

Divide 18 by 2. Does it divide exactly?
18 ÷ 2 = 9
Yes. 2 and the answer of the division (9) are factors of 18.
2 × 9 = 18
Write 2 and 9 in the grid, just inside the outside entries. 2 and 9 on the outside of a grid

3

Divide 18 by 3. Does it divide exactly?
18 ÷ 3 = 6
Yes. 3 and the answer of the division (6) are factors of 18.
3 × 6 = 18
Write 3 and 6 in the grid, just inside the previous entries. 3 and 6 on the outside of a grid

4

Divide 18 by 4. Does it divide exactly?
18 ÷ 4 = 4.5
No. The answer is not a whole number. 4 is not a factor.

5

Divide 18 by 5. Does it divide exactly?
18 ÷ 5 = 3.6
No. The answer is not a whole number. 5 is not a factor.

6

Divide 18 by 6. We already know that 6 is a factor of 18, it is already in the grid. We have found all the factors.

Answer:

The factors of 18 are 1, 2, 3, 6, 9 and 18.

Lesson Slides

The slider below shows another real example of finding the factors of a number.
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This page was written by Stephen Clarke.

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What Is a Factor?

A factor is a number which divides exactly into another number. The numbers that are multiplied together to make another number are factors.

Negative Factors

Numbers can have negative factors. If 1 and 2 are factors of 2 (since 1 × 2 = 2), then −1 and −2 are also factors, since:
−1 × −2 = 2
For the tests on this lesson, just use the positive factors.