Respuesta :

JakesBabe
The only common factor is 1. So that's the greatest. 
To get the Greates Common Factor (GCF) of 21 and 40 we need to factor each value first and then we choose all the copies of factors and multiply them: 

21:      3 740:   222 5 GCF:         The Greates Common Factor (GCF) is:   1