Bunuel - In this case I am a bit confused.
F is the center of the pentagon ABCDE ... So ABF form a triangle but not ACF, since a straight line drawn between AC will not pass through F.
I got 15 by doing 5 triangles formed with F as one of the points and then 5C3 thus 5+10 =15.
Please tell me what is wrong with my reasoning here.
acf does form a triangle. think of F immediately under A so drop a vertical line from a to f and then draw a line form a to c then connect c to f
the line from a to f stops at f and doesn't continue on to another letter. it angles over to c