New
New
Year 5

# Explain how to identify a prime factor of a number

I can explain how to identify a prime factor of a number.

New
New
Year 5

# Explain how to identify a prime factor of a number

I can explain how to identify a prime factor of a number.

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## Lesson details

### Key learning points

1. All numbers can be written as a product of 2 or more prime numbers.
2. A prime factor is a factor of a number which is prime.

### Common misconception

Pupils try to compose numbers additively using prime factors.

Ensure pupils are confident with finding the factors of a number first before extending to finding prime factors of known factors. Give time to building numbers with prime factors in arrays to help emphasise their multiplicative composition.

### Keywords

• Factor - A factor is a whole number which exactly divides another whole number.

• Prime factor - A prime factor is a factor of a number that is a prime number.

You might like to explore how prime factors are applied in the making and breaking of secret codes based on numbers. This is known as 'encryption' or 'cryptography'.
Teacher tip

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Starter quiz

### 6 Questions

Q1.
Match the number to the correct type.

3

6

4

Q2.
True or false: 19 is a prime number.
False
Q3.
Tick the prime numbers.
9
21
Q4.
Complete: 4 × 2 × 3 =
Q5.
What square number is represented by this incomplete factor bug?
Q6.
Match the expression to the correct product.
Correct Answer:4 × 5 × 5,100

100

Correct Answer:4 × 1 × 3,12

12

Correct Answer:4 × 3 × 5,60

60

Correct Answer:4 × 8 × 2,64

64

## Exit quiz

### 6 Questions

Q1.
True or false: 25 is a prime number.
True
Q2.
Tick the prime numbers.
9
12
15
Q3.
What are the prime factors shown in this factor bug?
1, 2, 3, 5, 6, 15
1, 2, 3, 5
2, 3, 5, 6
Q4.
The factor bug shows the factors of 16 Which of the calculations below correctly shows 16 decomposed into prime factors?
2 × 4 × 8 = 16
2 × 2 × 4 = 16
Correct answer: 2 × 2 × 2 × 2 = 16
Q5.
The factor bug shows the factors of 30 Which of the calculations below correctly shows 30 decomposed into prime factors?
Correct answer: 2 × 3 × 5 = 30
2 × 2 × 10 = 30
2 × 3 × 5 × 6 = 30
Q6.
What is the missing prime factor? 51 = 3 ×