Question: what is the greatest common factor in 21 24?
Answer: The prime factorization of 21 is: 3 x 7.
The prime factorization of 24 is: 2 x 2 x 2 x 3.
The prime factors and multiplicities 21 and 24 have in common are: 3.
3 is the gcf of 21 and 24.
gcf(21,24) = 3.