Say you belong to a group that has 20 members (N), and in order to get a particular benefit (B) you need 12 members (K) to contribute. This benefit (B) is a public good, which means that you will get to enjoy it whether you contribute or not. Assume that those who contribute to the provision of the benefit pay a cost, C. Of course, B > C.

If you know that exactly 15 members of the group (aside from yourself) will contribute, what should you do?

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