#### Answer

5

#### Work Step by Step

The GCF of 20 and 35 is 5.
To find, find the prime factors of each term.
20's factors are -20,-10,-5,-4,-2,-1,1,2,4,5,10,20.
For 35, they are -35,-7,-5,-1,1,5,7, and 35.
Look for the common factors. They are -5,-1,1, and 5.
The biggest one is 5, so that is the answer.