Given the following numbers

To find the greatest common factor, G.C.F.
The factor that can divide through two or more numbers evenly is the G.C.F
The factors of 20 and 32 are as follows

The common factors between 20 and 32 is

Hence, the GCF of 20 and 32 is 4
Alternatively
Finding the G.C.F using table to find the G.C.F of 20 and 32
Therefore, the G.C.F is

Hence, the G.C.F of 20 and 32 is 4