Question

Using prime factorisation, find the HCF and LCM of 12, 15, 21.

Answer 1

12 = 2 × 2 × 3 = 2² × 3

15 = 3 × 5

21 = 3 × 7

HCF = product of smallest power of each common prime factor in the numbers = 3

LCM = product of greatest power of each prime factor involved in the numbers

= 2² × 3 × 5 × 7

= 420