What is the least common factor of 9 12 and 15?

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

The factors of 12 are 1, 2, 3, 4, 6, and 12.

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

The common factors of 9, 12, and 15 are 1 and 3. Therefore, the least common factor (the smallest common factor) is 1.