Question: what are the first four common factors of 18 and 36 from least to greatest?
Answer: The factors of 36 are 36, 18, 12, 9, 6, 4, 3, 2, 1. The common factors of 18 and 36 are 18, 9, 6, 3, 2, 1, intersecting the two sets above. In the intersection factors of 18 ∩ factors of 36 the greatest element is 18. Therefore, the greatest common factor of 18 and 36 is 18.