Question

What number is a factor of both 60 and 90?

Answer 1

60 and 90 have 8 common factors (divisors): 1; 2; 3; 5; 6; 10; 15 and 30, out of which 3 prime factors: 2; 3 and 5.

Answer 2

Answer: 3 and 5

Hence the common factors of 30 and 75 are 1, 3, 5, 15, and their HCF is 15. The factors of 45 are 1, 3, 5, 9, 15, 45. Hence the HCF of 30, 75 and 45 is 15. The HCF of 60, 80, 90 and 100 is 10.