The greatest common factor (GCF) of 15 and 30 is: 15
Factors of 15: 1, 3, 5, 15
Factors of 30: 1, 2, 3, 5, 6, 10, 15
The common factors between the two numbers are 1, 3, 5, and 15, but considering 15 is the highest number out of them all, it is the greatest common factor.
