Twenty-one dots are evenly spaced on the circumference of a circle. How many combinations of three dots can we make from these 21 dots that do not form an equilateral triangle?
Choose one:	A) 1299	B) 1305	C) 1311	D) 1317	E) 1323

Rationale: the total number of ways we can choose three dots is 21 c 3 = 1330 . we can form seven equilateral triangles from these twenty - one dots . there are 1330 - 7 = 1323 combinations which do not form an equilateral triangle . the answer is e .
Answer: E