Question: what is the greatest common factor of 12 and 56?
Answer: The factors of 56 are 56, 28, 14, 8, 7, 4, 2, 1. The common factors of 12 and 56 are 4, 2, 1, intersecting the two sets above. In the intersection factors of 12 ∩ factors of 56 the greatest element is 4. Therefore, the greatest common factor of 12 and 56 is 4.