The greatest common factor (GCF) of 48 and 78 is: 6
Factors of 48: 1, 2, 3, 4, 6, 8, 12, 16, 24, 48
Factors of 78: 1, 2, 3, 6, 13, 26, 39
The common factors between the two numbers are 1, 2, 3, and 6, but considering 6 is the highest number out of them, it is the greatest common factor.