The GCF of 8 and 18 is: 2
To find the greatest common factor of any numbers, you list the factors (numbers that you can multiply by to receive the given number) and see which number is common.
Factors of 8: 1, 2, 4, 8
Factors of 18: 1, 2, 3, 6, 9, 18
So, our common factors are 1 and 2, but since we are looking for the greatest common factor, the greatest would be 2.