Explain how to identify a prime factor of a number | Maths

Starter quiz

Match the number to the correct type.

Prime number

⇔

3 ✓

Composite number

⇔

6 ✓

Square number

⇔

4 ✓
True or false: 19 is a prime number.

True ✓
False
Tick the prime numbers.

3 ✓

7 ✓

9

17 ✓

21
Complete: 4 × 2 × 3 = ______

'24' ✓
What square number is represented by this incomplete factor bug?

'36' ✓
Match the expression to the correct product.

4 × 5 × 5

⇔

100 ✓

4 × 1 × 3

⇔

12 ✓

4 × 3 × 5

⇔

60 ✓

4 × 8 × 2

⇔

64 ✓

Exit quiz

True or false: 25 is a prime number.

True
False ✓
Tick the prime numbers.

9

11 ✓

12

15

17 ✓
What are the prime factors shown in this factor bug?

1, 2, 3, 5, 6, 15

1, 2, 3, 5

2, 3, 5 ✓

2, 3, 5, 6
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

2 × 2 × 2 × 2 = 16 ✓
The factor bug shows the factors of 30 Which of the calculations below correctly shows 30 decomposed into prime factors?

2 × 3 × 5 = 30 ✓

2 × 2 × 10 = 30

2 × 3 × 5 × 6 = 30
What is the missing prime factor? 51 = 3 × ______

'17' ✓

Worksheet

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Lesson Details

Key learning points

All numbers can be written as a product of 2 or more prime numbers.
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.