Definition of HCF (Highest Common Factor):

The largest positive integer which divides two or more integers without any remainder is called Highest Common Factor (HCF) or Greatest Common Divisor or Greatest Common Factor (GCF).

(i) Prime factorization of 75 and 243 are:

75 = 3 × 5 × 5

243 = 3 × 3 x 3 × 3 × 3

From above prime factorization we got that the highest common factor of 75 and 243 is 3

(ii) Prime factorization of 240 and 6552 are:

240 = 2 × 2 ×2 × 2 × 3 × 5

6552 = 2 × 2 × 2 × 3 x 3 × 7 × 13

From above prime factorization we got that the highest common factor of 240 and 6552 is 2×2×2×3 ⇒ 24

(iii) Prime factorization of 155 and 1385 are:

155 = 5 × 31

1385 = 5 × 277

From above prime factorization we got that the highest common factor of 155 and 1385 is 5

(iv) Prime factorization of 100 and 190 are:

100 = 2 × 2 × 5 × 5

190 = 2 × 5 ×19

From above prime factorization we got that the highest common factor of 155 and 1385 is 2×5 ⇒ 10

(v) Prime factorization of 105 and 120 are:

105 = 3 × 5 × 7

120 = 2 × 2 × 2 × 3 × 5

From above prime factorization we got that the highest common factor of 105 and 120 is 3×5 ⇒ 15