1. The problem statement, all variables and given/known data If we want to use positive integers from 1 until 7 to form a ring in order. Since 1 and 7 are adjacent to each other in the ring. Due to their neighbouring position, 1 and 7 are also considered as neighbour numbers. Then if we want to pick 3 non-neighbouring numbers from this ring of 7 numbers, how many different solutions are there? 2. Relevant equations C(n,r) = n! / (r! * (n-r)!) 3. The attempt at a solution Brute force. Is there a quicker method to solve this problem?