What is the common factor of 39 and 52,
1 and 13
What is the common factor of 150 and 255
15
What is the common factor of 150 and 500
The greatest common factor is 50. Then their factors are all the factors of 50
The common factor of 78 and 91
78=2×3×13
91=7×13
Common factor = 1,13