Year 6 · Maths · Four operations · Lesson 5

Common factors, multiples and primes

Find common factors, the highest common factor, common multiples and the lowest common multiple; identify primes, squares and cubes; solve word problems.

21-minute video lesson

Teaching, worked examples and 20 practice questions solved step by step.

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What your child will learn

Find common factors and the HCF
Find common multiples and the LCM
Identify prime numbers to 100
Recognise square and cube numbers
Choose HCF or LCM in problems

The method

List factors or multiples of each.
Circle the ones in both.
HCF = highest; LCM = lowest.
Word problem: factor or multiple?

Key words: factor, multiple, common, prime, square number, cube number.

Worked examples

The first three practice questions from the lesson, with every step.

Question 1

Find the common factors of 8 and 12. What is the highest common factor?

Step 1: Factors of 8: 1, 2, 4, 8
Step 2: Factors of 12: 1, 2, 3, 4, 6, 12
Step 3: In both: 1, 2, 4

Answer: 1, 2, 4; HCF = 4

Question 2

Find the common factors of 15 and 20. What is the highest common factor?

Step 1: Factors of 15: 1, 3, 5, 15
Step 2: Factors of 20: 1, 2, 4, 5, 10, 20
Step 3: In both: 1, 5

Answer: 1, 5; HCF = 5

Question 3

Find the common factors of 16 and 24. What is the highest common factor?

Step 1: Factors of 16: 1, 2, 4, 8, 16
Step 2: Factors of 24: 1, 2, 3, 4, 6, 8, 12, 24
Step 3: In both: 1, 2, 4, 8

Answer: 1, 2, 4, 8; HCF = 8