What is the least common factor of 9 and 15?

Most of the time, math questions are about the greatest common factor or the least common multiple, not the least common factor. The least common factor of any two numbers would typically be 1.

The factors of 15 are 1, 3, 5, and 15.

The factors of 9 are 1, 3, and 9.

The greatest common factor is 3.

The prime factors of 15 are 3 and 5.

The prime factors of 9 are 3 and 3.

So, take the 3 and 5 prime factors of 15, and then the second 3 prime factor of 9, multiply them together, so 3 x 5 x 3 = 45 is the least common multiple.