Question: what is the greatest common factor gcf of 45 and 90?
Answer: The common factors of 45 and 90 are 45, 15, 9, 5, 3, 1, intersecting the two sets above. In the intersection factors of 45 ∩ factors of 90 the greatest element is 45. Therefore, the greatest common factor of 45 and 90 is 45.