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Hard · Game Theory & Logic · Quant Trader interview question · game-theory, probability, expected-value, logic
100 prisoners are isolated in separate cells. There is a central room with a single lightbulb. Initially, the lightbulb is off. At random times, but with each prisoner equally likely to be chosen, a prisoner is allowed to enter the central room. The prisoner in the room can observe the current state of the lightbulb (on or off) and can toggle it if desired. The prisoner can also choose to make an announcement: "All prisoners have now been in the room." If the announcement is correct, all prisone