Greatest Common Divisor (or Factor)The greatest common factor, or GCF, is the greatest factor that divides two or more numbers. To find the GCF of two numbers: List the prime factors of each number. Multiply those factors both numbers have in common. If there are no common prime factors, the GCF is 1.
Example: To find the GCF of 24 and 32
Prime factors of 24 : 2, 2, 2, 3
Prime factors of 32 : 2, 2, 2, 2, 2
GCF is 2 x 2 x 2 which is equal to 8.