SStudy Room

Calculators · Numbers

HCF and LCM

The highest common factor and lowest common multiple of 2 to 5 numbers, by prime factorisation.

HCF = 6, LCM = 1260

The working

  1. 84 = 2² × 3 × 7.
  2. 90 = 2 × 3² × 5.
  3. HCF: the primes in every number, each with its smallest power: 2 × 3 = 6.
  4. LCM: every prime that appears, each with its largest power: 2² × 3² × 5 × 7 = 1260.
  5. Check: HCF × LCM = 6 × 1260 = 7560, and 84 × 90 = 7560.