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.