What is the greatest common factor of 15 and 20?

The greatest common factor of two numbers is the largest number that divides both of them without leaving a remainder.

To find the greatest common factor of 15 and 20, we can list the factors of each number:

• The factors of 15 are: 1, 3, 5, 15
• The factors of 20 are: 1, 2, 4, 5, 10, 20

The common factors of 15 and 20 are 1 and 5. Therefore, the greatest common factor of 15 and 20 is 5.