HCF and LCM of 28 and 42
For 28 and 42, the highest common factor is 14 and the least common multiple is 84.
HCF = 14. LCM = 84.
These two results answer different questions: the HCF is the largest shared divisor, while the LCM is the smallest positive shared multiple.
14 divides both 28 and 42 exactly.
84 is the first positive number both values divide into.
Factors of 28 and 42
- Factors of 28
- 1, 2, 4, 7, 14, 28
- Factors of 42
- 1, 2, 3, 6, 7, 14, 21, 42
- Common factors
- 1, 2, 7, 14
The common factors are the values that divide both numbers with no remainder. The greatest one is 14, so HCF(28, 42) = 14.
Prime factorisation working
For the HCF, use only the shared primes at their smallest powers: 2 × 7 = 14. For the LCM, use every prime needed at its greatest power: 2² × 7 × 3 = 84.
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What these answers mean
Use the HCF when you want the largest equal grouping size or to simplify a fraction. Use the LCM when you want the first time two repeating schedules meet, or a least common denominator for fractions.
This page is a worked answer for 28 and 42. It is not a replacement for checking your own question: use the calculators above for other inputs.