What is it
HCF (Highest Common Factor) is the largest number that divides exactly into two or more numbers, while LCM (Lowest Common Multiple) is the smallest number that both numbers divide into exactly.
Why it matters
HCF and LCM aren't just abstract exercises — HCF is used to simplify fractions to their lowest terms, and LCM is essential for adding and subtracting fractions with different denominators, a skill tested constantly at KS2 and GCSE.
Exam tip
Listing the multiples or factors of each number systematically, rather than guessing, avoids the most common error — missing one further down the list.
Related topics
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