Question: what is the greatest common factor in 9 and 49?
Answer: The factors of 9 are 9, 3, 1. The factors of 49 are 49, 7, 1. The common factors of 9 and 49 are 1, intersecting the two sets above. In the intersection factors of 9 ∩ factors of 49 the greatest element is 1. Therefore, the greatest common factor of 9 and 49 is 1.