Final answer:
The greatest common factor of 40 and 60 is 20.
Step-by-step explanation:
The greatest common factor (GCF) of 40 and 60 can be found by listing the factors of both numbers and identifying the largest factor they have in common.
The factors of 40 are: 1, 2, 4, 5, 8, 10, 20, 40.
The factors of 60 are: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60.
From the lists above, the largest factor that 40 and 60 have in common is 20. Therefore, the greatest common factor of 40 and 60 is 20.