Question: what is the highest common factor of 36?
Answer: 1, 2, 3, 4, 6, 9, 12, 18, and 36. 1, 2, 3, 6, 9, 18, 27, and 54. Although the numbers in bold are all common factors of both 36 and 54, 18 is the greatest common factor. The second method to find the greatest common factor is to list the prime factors, then multiply the common prime factors.