Make Math Work

Greatest Common Factor

Usage: GCF Numerator, Denominator
GCD Numerator, Denominator

The GCF command will determine the greatest common factor of the two numbers entered. This factor is useful for reducing fractions.

To find the greatest common factor, enter GCD and two numbers separated by a comma, for example, GCF 48, 60.

The prime factorization of each number is shown with prime factors common to both numbers displayed in red. Multiplying these common prime factors yields the greatest common factor. Multiply the common prime factors for your choice of either entered number, not the prime factors for both entered numbers, otherwise you would get double the greatest common factor.

Some pairs of numbers may not have a common factor.

Examples:
GCF 40, 50 returns 10.
GCF 17, 20 returns no common factor, since 17 is prime.
GCF 15, 22 returns no common factor, since 15 and 22 do not share a common factor.