Question: what is the greatest common factor of 49 and 70?
Answer: The factors of 70 are 70, 35, 14, 10, 7, 5, 2, 1. The common factors of 49 and 70 are 7, 1, intersecting the two sets above. In the intersection factors of 49 ∩ factors of 70 the greatest element is 7. Therefore, the greatest common factor of 49 and 70 is 7.