# Prime Factorisations

In this worksheet, students select the correct prime factorisation for the given numbers.

Key stage:  KS 3

Curriculum topic:   Number

Curriculum subtopic:   Use Concepts and Vocabulary for All Numbers

Difficulty level:

### QUESTION 1 of 10

The list of prime numbers starts as follows:

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37........

All other whole numbers are known as composite and can be written as the product of prime factors.

This is known as  prime factorisation.

Examples

35 = 5 x 7

14 = 2 x 7

28 = 2 x 2 x 7

24 = 2 x 2 x 2 x 3

Writing 24 = 2 x 3 x 4 is correct but it is not a full prime factorisation because the 4 is not prime.

Select the correct prime factorisation for:

15

1 x 5

3 x 5

3 x 3 x 5

1 x 15

Select the correct prime factorisation for:

30

2 x 15

3 x 10

3 x 3 x 5

2 x 3 x 5

Select the correct prime factorisation for:

24

2 x 12

2 x 2 x 2 x 3

2 x 3 x 4

3 x 8

Select the correct prime factorisation for:

25

25

5 x 5

2 x 5

5 x 20

Select the correct prime factorisation for:

36

2 x 2 x 3 x 3

4 x 9

3 x 3 x 5

5 x 7 + 1

Select the correct prime factorisation for:

20

2 x 2 x 3

4 x 5

2 x 2 x 5

2 x 10

Select the correct prime factorisation for:

16

2 x 2 x 3

4 x 4

2 x 2 x 4

2 x 2 x 2 x 2

Select the correct prime factorisation for:

40

2 x 2 x 10

4 x 2 x 5

2 x 2 x 5

2 x 2 x 2 x 5

Select the correct prime factorisation for:

42

2 x 2 x 7

2 x 3 x 7

2 x 3 x 5

2 x 2 x 2 x 7

Select the correct prime factorisation for:

45

2 x 2 x 5

2 x 3 x 5

3 x 3 x 5

2 x 2 x 2 x 5

• Question 1

Select the correct prime factorisation for:

15

3 x 5
• Question 2

Select the correct prime factorisation for:

30

2 x 3 x 5
• Question 3

Select the correct prime factorisation for:

24

2 x 2 x 2 x 3
• Question 4

Select the correct prime factorisation for:

25

5 x 5
• Question 5

Select the correct prime factorisation for:

36

2 x 2 x 3 x 3
• Question 6

Select the correct prime factorisation for:

20

2 x 2 x 5
• Question 7

Select the correct prime factorisation for:

16

2 x 2 x 2 x 2
• Question 8

Select the correct prime factorisation for:

40

2 x 2 x 2 x 5
• Question 9

Select the correct prime factorisation for:

42

2 x 3 x 7
• Question 10

Select the correct prime factorisation for:

45

3 x 3 x 5
---- OR ----

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