01
Always find both, always
A word problem about bells ringing together is LCM. Sharing into rows is HCF. The child finds both and circles one.
Topic hub
LCM and HCF
HCF is the largest number that divides both; LCM is the smallest number both divide into. Children struggle when they can run a prime-factor recipe and cannot say which one a word problem wants.
Why this concept matters
The recipe is cheap. The decision is the maths.
Misconceptions, in the order we see them
02
Prime factors are the answer
They stop before multiplying back.
03
Two primes: HCF is the smaller
HCF is 1. This feels like a trick rather than a definition.
Which classes cover this
Related: Fractions · Decimals · Percentages · Ratio and proportion · Integers
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