The greatest common factor of 20 and 30 is 10. This is because 10 is the largest number that when it is used to divide 20 or 30, it equals a whole number.
The simple way for us to solve is to write down the factors of both numbers, find the factors that match for both numbers, and see which is the largest out of those that match.
20: 1,2,4,5,10,20
30: 1,2,3,5,6,10,15,30
Using that logic, we can see that 10 is the greatest factor that the numbers share.
