choose 3 objects from 28 placed along a circle.

Question

28 objects are placed along a circle at equal distances.In how mnay ways can 3 objects choosen from among them so that no two of three choosen objects are adjacent nor diametrically opposite

Answer 1

(28/3) - 28 - ((28/1) × (24/1)) - (14 × (22/1))

 

I have just replaced the values in the formula see if that helps and left for you to put in the calculator. 

Answer 2

I found a similar question on this website. all you need is to change the object number on the formula.

 

http://blog.cheenta.com/2015/12/07/36-objects-in-a-circle-regional-math-olympiad-2015-solution-of-problem-4/