What is the GCF of 280 and 420 and how?

Answer 1

The factors of 280 are:

1, 2, 4, 5, 7, 8, 10, 14, 20, 28, 35, 40, 56, 70, 140, 280

The factors of 420 are:

1, 2, 3, 4, 5, 6, 7, 10, 12, 14, 15, 20, 21, 28, 30, 35, 42, 60, 70, 84, 105, 140, 210, 420

The common factors are:

1, 2, 4, 5, 7, 10, 14, 20, 28, 35, 70, 140

The Greatest Common Factor:

GCF = 140

Answer 2

GCF(280, 420) = 140

140*2 = 280

140*3 = 420

and, since 2 and 3 are co-prime, there cannot be a greater common factor.