There are 10 prisoners are in 10 different cells of a prison. There is no way in which they can communicate with each other.
Each night, the warden picks one of the 10 prisoners and that prisoner is supposed to spend the entire night in the central living room. There is one bulb in the living room which can be switched on or off.
Warden puts a condition, “If any of the prisoner can tell with certainty, that all the other prisoners have spent night in the central living room, then he will free all of them. But, If the prisoner says that all the other have spent night in the living room, but that is not true, then all the prisoners will be killed”. Thus, the assertion should only be made if the prisoner is 100% certain of its validity.
Before the random picking begins, the prisoners are allowed to get together and make some strategy. But, once the strategy is made, then a prisoner cannot communicate with any other prisoner.
What plan should they agree on, so that eventually, someone will make a correct assertion?