HCF and LCM: GCSE Maths revision
HCF is the largest number that divides into both. LCM is the smallest number that both divide into. Prime factor trees make both reliable.
Using prime factors
HCF: multiply the primes that appear in both, using the lowest power. LCM: every prime that appears in either, using the highest power.
HCF and LCM of 12 and 18
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
HCF of 8 and 12
LCM of 6 and 8
Write 60 as a product of primes
HCF of 24 and 36
LCM of 9 and 12
Common mistakes
- Mixing up HCF and LCM.
- Missing a repeated prime in the product of primes.
Answers and working
Frequently asked questions
When do exam questions use HCF?
Splitting into equal groups, simplifying ratios, or “largest tile that fits” problems.
Learn, try, get feedback, fix the mistake
ReviseEasy covers GCSE Maths, Combined Science, Triple Science, English Language and English Literature — then drills the topics you keep dropping marks on.
Practise more on ReviseEasy →Related revision
More GCSE revision
ReviseEasy is a GCSE revision website, not a Maths-only site. Lessons, quizzes and flashcards are live for Maths, Combined Science, Triple Biology, Chemistry and Physics, English Language and English Literature. History, Geography and languages are next.