Question

Using prime factorisation, find the HCF and LCM of 21, 28, 36, 45.

Answer 1

21 = 3 × 7

28 = 2 × 2 × 7 = 2² × 7

36 = 2 × 2 × 3 × 3 = 2² × 3²

45 = 5 × 3 × 3 = 5 × 3²

HCF = product of smallest power of each common prime factor in the numbers = 1

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

= 2² × 3² × 5 × 7

= 1260