what is the gcf of 9 and 18

The GCF (Greatest Common Factor) of 9 and 18 is 9. One way to find the GCF of two numbers is to compare their prime factorizations. The prime factorization of 9 is 3 x 3, and the prime factorization of 18 is 2 x 3 x 3. The common factor is 3 x 3, which equals 9, so the GCF of 9 and 18 is 9.