Six dots are evenly spaced on the circumference of a circle. How many combinations of three dots can we make from these 6 dots that do not form an equilateral triangle?
Select:
A) 18 B) 17 C) 16 D) 15 E) 14

Rationale: the total number of ways we can choose three dots is 6 c 3 = 20 . we can form two equilateral triangles from these six dots . there are 20 - 2 = 18 combinations which do not form an equilateral triangle . the answer is a .
Answer: A