(i) 18, 24.
Prime factorisation of 18 = 2 × 3 × 3
Prime factorisation of 24 = 2 × 2 × 2 × 3
Common factors of 18 and 24 = 2 × 3 = 6
HCF (18, 24) = 6
(ii) 51, 85
Prime factorisation of 51 = 3 × 17
Prime factorisation of 85 = 5 × 17
Common factors of 51 and 85 = 17
HCF (51, 85) = 17
(iii) 61, 76
Prime factorisation of 61 = 1 × 61
Prime factorisation of 76 = 2 × 2 × 19 × 1
Common factors of 61 and 76 = 1
HCF (61, 76) = 1
(iv) 84, 120
Prime factorisation of 84 = 2 × 2 × 3 × 7
Prime factorisation of 120 = 2 × 2 × 2 × 3 × 5
Common factors of 84 and 120 = 2 × 2 × 3
HCF (84, 120) = 12
(v) 27, 45, 81
Prime factorisation of 27 = 3 × 3 × 3
Prime factorisation of 45 = 3 × 3 × 5
Prime factorisation of 81 = 3 × 3 × 3 × 3
Common factors of 27, 45, 81 = 3 × 3 = 9
HCF (27, 45, 81) = 9
(vi) 45, 55, 95
Prime factorisation of 45 = 3 × 3 × 5
Prime factorisation of 55 = 5 × 11
Prime factorisation of 95 = 5 × 19
Common factors of 45, 55, 95 = 5
HCF (45, 55, 95) = 5
