What is the greatest common factor of 15 and 23?

The GCF of 15 and 23 is 1 because 23 is a prime and has no factors other than 1 and itself. 1, they have no common factors except 1

Using Euclid's Algorithm

23=(15)(1) + 8 =>

15=(8)(1)+7 =>

8=(7)(1)+1 =>

7=(1)(7)

Thus the highest common factor of 15 and 23 is 1.