There are five pirates on a ship with 100 gold coins of booty, and they are trying to divide the coins between them. The method that they have agreed is that the oldest pirate proposes a distribution of the coins and all the pirates vote on the proposal. If 50% or more of the pirates agree with the proposal, it is accepted and the coins distributed. If not then the pirate that made the proposal is thrown overboard and the oldest remaining pirate proposes a distribution of coins.
The pirates don't like each other, so if a pirate would get the same number of coins however he votes, he will vote against to kill the proposing pirate.
If everyone votes logically, what happens?
Let's work backwards from two pirates.
In this case the oldest proposes that he receives all 100 coins and his vote is 50% so he gets 100 coins.
With three pirates the eldest will propose a split of 99, 0 and 1. The youngest pirate will accept this, because if he doesn't there will be only two pirates left, and he gets nothing.
With four pirates the eldest will propose a split of 99, 0, 1 and 0. As with three pirates, the second youngest will support this, otherwise he'll get nothing.
So with the initial five pirates a split of 98, 0, 1, 0 and 1 will be supported by three pirates, the eldest, and the two who receive one coin each who would get nothing on the four-pirate vote.