What is the greatest common factor of 28 42 and 56?

When finding the GCF of a set of numbers, firstly express each number as a product of its prime factors.

28 = 2 x 2 x 7

42 = 2 x 3 x 7

56 = 2 x 2 x 2 x 7

The factors that each number has in common are 2 and 7.

The Greatest Common Factor is therefore 2 x 7 = 14