21 , 28

Find the common factors for the numerical part:

21,28

The factors for 21 are all numbers between 1 and 21, which divide 21 evenly.

Check numbers between 1 and 21

Find the factor pairs of 21 where x⋅y=21.

xy12137

List the factors for 21.

1,3,7,21

1,3,7,21

The factors for 28 are all numbers between 1 and 28, which divide 28 evenly.

Check numbers between 1 and 28

Find the factor pairs of 28 where x⋅y=28.

xy12821447

List the factors for 28.

1,2,4,7,14,28

1,2,4,7,14,28

List all the factors for 21,28 to find the common factors.

21: 1,3,7,21

28: 1,2,4,7,14,28

The common factors for 21,28 are 1,7.

1,7

The GCF (HCF) of the numerical factors 1,7 is 7.

7

Find the GCF 21 , 28