AIME
2014


Problem - 87
Let the set $S = {P_1, P_2, \dots, P_{12}}$ consist of the twelve vertices of a regular $12$-gon. A subset $Q$ of $S$ is called 'communal' if there is a circle such that all points of $Q$ are inside the circle, and all points of $S$ not in $Q$ are outside of the circle. How many communal subsets are there? (Note that the empty set is a communal subset.)

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