How do you figure greatest common factor?

Answer 1

To find the greatest common factor (GCF), first find the prime factorization of the two numbers.

The GCF is the product of all of the prime factors the two numbers have in common.

If two numbers have no common factors, the GCF is 1. (Since all numbers are divisible by 1.)

Example: Find the GCF of 60 and 24.

Prime factors of 60: 2, 2, 3, 5

Prime factors of 24: 2, 2, 2, 3

Common factors: 2, 2, 3

GCF: 2x2x3=12

Example: Find the GCF of 17 and 21.

Prime factors of 17: 17

Prime factors of 21: 3, 7

Common factors: None (1).

GCF: 1