Question: what is the greatest common factor of 36 and 39?
Answer: The prime factorization of 36 is: 2 x 2 x 3 x 3.
The prime factorization of 39 is: 3 x 13.
The prime factors and multiplicities 36 and 39 have in common are: 3.
3 is the gcf of 36 and 39.
gcf(36,39) = 3.