What number is a common factor of 15 18 and 30?

Answer 1

By its very definition, a single number cannot have a greatest common factor. The word "common" is there to indicate common to more than one integer.

Of the 11 pairs, triplets and quads that can be drawn from the four numbers,

6 have GCF = 3,

4 have GCF = 6, and

1 has GCF = 15.

Answer 2

The GCF is 3.

Answer 3

1 and 3

Answer 4

It is: 1