Question: what is the greatest common factor in 14 and 15?
Answer: The factors of 14 are 14, 7, 2, 1. The factors of 15 are 15, 5, 3, 1. The common factors of 14 and 15 are 1, intersecting the two sets above. In the intersection factors of 14 ∩ factors of 15 the greatest element is 1. Therefore, the greatest common factor of 14 and 15 is 1.