The greatest common factor (GCF) of 9, 18, and 21 is 3.
To find the GCF, we first need to determine the factors of each number:
- Factors of 9: 1, 3, 9
- Factors of 18: 1, 2, 3, 6, 9, 18
- Factors of 21: 1, 3, 7, 21
Next, we look for the common factors among all three numbers. The common factors are:
- 1
- 3
Among these common factors, the greatest one is 3. Therefore, the greatest common factor of 9, 18, and 21 is 3.