What is the greatest common factor of 65 and 91

13 is the greatest common factor of 65 and 91.

So,

First, we find the prime factored form (P. F. F.) of 65 and 91.

P. F. F. of 65: 5 * 13

P. F. F. of 91: 7 * 13

Find the common numbers

13

13 = G. C. F.

Note: This method works for finding any G. C. F. (find common primes)