Question: what is the greatest common factor for 6 and 30?
Answer: The prime factorization of 6 is: 2 x 3.
The prime factorization of 30 is: 2 x 3 x 5.
The prime factors and multiplicities 6 and 30 have in common are: 2 x 3.
2 x 3 is the gcf of 6 and 30.
gcf(6,30) = 6.