The greatest common factor (GCF) of 72 and 81 is 9.
To find the GCF, we first list the factors of each number:
- Factors of 72: 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72
- Factors of 81: 1, 3, 9, 27, 81
Next, we identify the common factors between these two lists, which are 1, 3, and 9. The greatest of these common factors is 9.
Thus, the GCF of 72 and 81 is 9.