Find the prime factorization of each value.
21 is 73
30 is 310 which can be further broken down into 325
44 is 411 which can be further broken down into 22*11
What do they share in common?
21 and 30 each have a 3 in common.
Therefore the GCF(21, 30) = 3.
21 and 44 share a 2 in common.
But if we're looking at all three of them together, they share nothing in common.
