Question: what is the greatest common factor of 28 and 72?
Answer: The prime factorization of 28 is: 2 x 2 x 7. The prime factorization of 72 is: 2 x 2 x 2 x 3 x 3. The prime factors and multiplicities 28 and 72 have in common are: 2 x 2. 2 x 2 is the gcf of 28 and 72. gcf(28,72) = 4.