Question: what is the highest common factor of 11 and 77?
Answer: The factors of 11 are 11, 1. The factors of 77 are 77, 11, 7, 1. The common factors of 11 and 77 are 11, 1, intersecting the two sets above. In the intersection factors of 11 ∩ factors of 77 the greatest element is 11. Therefore, the greatest common factor of 11 and 77 is 11.