Question

What is the greatest common factor of 21 and 55

Answer 1

Go about this by finding the factors of 55 and 21.

21 | 1,3,7,21
55 | 1,5,11,55

1 is the greatest common factor.

:)

Answer 2

So to get the Greatest Common Factor (GCF) of 55 and 21 we must need to factor each value first and then we choose all the copies of factors and multiply each of them here is what i mean: 

55:    5 1121:   3 7     

The Greatest Common Factor (GCF) is:   1