Question: what is the greatest common factor of 3 and 27?
Answer: The factors of 27 are 27, 9, 3, 1. The common factors of 3 and 27 are 3, 1, intersecting the two sets above. In the intersection factors of 3 ∩ factors of 27 the greatest element is 3. Therefore, the greatest common factor of 3 and 27 is 3.