Question: what is the greatest common factor for 69 and 23?
Answer: The factors of 23 are 23, 1. 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.