Question: what is the greatest common factor of 8 and 20 using prime factorization?
Answer: The prime factorization of 20 is: 2 x 2 x 5. The prime factors and multiplicities 8 and 20 have in common are: 2 x 2. 2 x 2 is the gcf of 8 and 20. gcf(8,20) = 4.