Maths Library

Prime Numbers and Prime Factorisation: Year 5 maths

Identify prime and composite numbers and decompose integers into their prime factorisations. Pupils construct factor trees and write prime factor expressions using index notation.

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What this covers

Prime Numbers and Prime Factorisation is taught in Year 5 (age 10 to 11) as a topic to introduce. It sits in the Number strand.

Worked example

Write 60 as a product of its prime factors using index notation.

  1. Divide 60 by lowest prime 2: 60 = 2 × 30
  2. Divide 30 by 2: 30 = 2 × 15
  3. Divide 15 by 3: 15 = 3 × 5 (both are prime)
  4. Write in index form: 2^2 × 3 × 5

Answer: 2^2 × 3 × 5

Difficulty scale

The sheet generator offers five difficulty settings for this topic.

  1. Identify prime and composite numbers up to 30
  2. Identify prime numbers up to 100
  3. Find prime factors of 2-digit numbers using factor trees
  4. Write prime factorisation of numbers up to 150 in index form
  5. Find prime factorisations of numbers up to 500 and solve prime-based puzzles

Common mistakes

  • Thinking 1 is a prime number or that all odd numbers are prime
  • Leaving composite factors in a prime factor tree (e.g. writing 60 as 4 * 15)

Curriculum links

Indicative matches to Australian Curriculum v9. Check wording and codes against the official document.

  • AC9M5N01 Identify and describe properties of prime, composite, square, and triangular numbers.

Sample sheet and answers

Six questions at the level's usual difficulty. Open the editor to change, add or regenerate any of them.

Prime Numbers and Prime Factorisation

Year 5 maths

Qs
6
Marks
6
NameDateScore / 6
1.
Is 9 a prime number? Write yes or no.
[1]
2.
Is 18 a prime number? Write yes or no.
[1]
3.
Is 9 a prime number? Write yes or no.
[1]
4.
Is 14 a prime number? Write yes or no.
[1]
5.
Is 9 a prime number? Write yes or no.
[1]
6.
Is 20 a prime number? Write yes or no.
[1]

Answer key

  1. no9 is divisible by 3, so it has another factor
  2. no18 is divisible by 2, so it has another factor
  3. no9 is divisible by 3, so it has another factor
  4. no14 is divisible by 2, so it has another factor
  5. no9 is divisible by 3, so it has another factor
  6. no20 is divisible by 2, so it has another factor