The GCF is 1.
The GCF is 3.
21 and 42 have a GCF of 21. 40 and 80 have a GCF of 40. The GCF of 21 and 40 is 1.
The GCF is 1.
The GCF is 1.
The GCF is 21.
The GCF is 1.The GCF of 14, 21 and 24 is 1.
The GCF is 1.
The GCF is 1.
The GCF is 21.
The GCF is 3.
The GCF is 1.
The GCF is 21.
The GCF is 1.
The GCF is 1.
The GCF is 3.
The greatest common factor of 21 and 63 is 21.Since 21 is a factor of 63, it is automatically the GCF.