Question: what is the greatest common factor of 69 and 23?
Answer: The factors of 69 are 69, 23, 3, 1. The common factors of 23 and 69 are 23, 1, intersecting the two sets above. In the intersection factors of 23 ∩ factors of 69 the greatest element is 23. Therefore, the greatest common factor of 23 and 69 is 23.