Find a common factor
- List factors of each number.
- Circle factors in both lists.
- Choose the highest if asked for the HCF.
Answer: HCF of 20 and 30 is 10
🔢 Number
Common factors
Learn common factors with a GCSE-style explanation, help guide, worked example, practice question and flashcards.
Global XP
Level 10 / 100 XP
1. Explanation
Key idea
- Common factors is part of number and appears often in KS3–GCSE maths.
- Common factors divide exactly into two or more numbers.
- Use the worked model, help guide, interactive question and flashcards to practise common factors until the steps feel automatic.
Real-life examples
- Shopping, sport, travel, science, design and everyday decisions all use this skill.
2. Visual
Common factors learning map
Understand the key idea → follow the help guide → practise a question → check your method → build speed with flashcards.
3. Help guide
How to tackle Common factors
- Learn the rule: Common factors divide exactly into two or more numbers.
- Worked model: List factors of each number. Circle factors in both lists. Choose the highest if asked for the HCF.
- Try the interactive question without looking at the answer first.
- Use the flashcards to test the rule, the method and a common check.
4. Worked examples
Step-by-step working
5. Interactive questions
Try it yourself
What is the highest common factor of 18 and 24?
6. Flashcards
Master quick recall
Flip each card, then choose whether you know it or need more practice.
0 mastered
FrontRule for Common factors
BackCommon factors divide exactly into two or more numbers.
FrontExample answer: What is the highest common factor of 18 and 24?
BackFactors of 18 include 1, 2, 3, 6, 9, 18. Factors of 24 include 1, 2, 3, 4, 6, 8, 12, 24. The highest common factor is 6.
FrontCommon check for Common factors
BackCheck units/notation, compare with an estimate, and make sure the answer matches the question.
7. Finish
Complete this topic
When you have read the examples, tried the question and reviewed flashcards, claim your topic completion XP.