Greatest common factor for group of terms?

Question

10a, 9b, and 77c

I get the answer 1 for this problem, and i'm told its incorrect because a prime number is not a natural number? I'm lost... help?

Answer 1

there is no number that goes into 10, 9 and 77 except 1.  9 is only divisable by 1, 9 and 3 and none of those go into 10 evenly except 1.  So, if your teacher isn't accepting 1, then the answer is nothing, there is not gcf for that particular group of terms.

Answer 2

I don't think there is a greatest common factor.

Answer 3

What you've been told is disastrously wrong. All prime numbers are natural numbers (as are the composite numbers) and 1, though neither prime nor composite, is a natural number. In fact your answer was correct.