Question: what is a common factor between 8 and 7?
Answer: The factors of 8 are 8, 4, 2, 1. The common factors of 7 and 8 are 1, intersecting the two sets above. In the intersection factors of 7 ∩ factors of 8 the greatest element is 1. Therefore, the greatest common factor of 7 and 8 is 1.