Question: what is the largest common factor of 14 and 91?
Answer: The factors of 14 are 14, 7, 2, 1. The factors of 91 are 91, 13, 7, 1. The common factors of 14 and 91 are 7, 1, intersecting the two sets above. In the intersection factors of 14 ∩ factors of 91 the greatest element is 7. Therefore, the greatest common factor of 14 and 91 is 7.