Three guests check in to a hotel, like we just checked in here. The guy behind the desk says it’s $30, so they each pay ten. Later the clerk realizes… - Mark Watson

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Three guests check in to a hotel, like we just checked in here. The guy behind the desk says it’s $30, so they each pay ten. Later the clerk realizes he overcharged them: it should have been $25. So he gives the bellboy five bucks to return to the guests. Obviously he can’t divide it equally. He keeps $2 for himself. Gives one dollar back to everyone. So they have all paid nine dollars now, yes?’ Everyone agreed that this was true. ‘And the bellboy has two. So they’ve paid nine times three, twenty-seven. He has two. But we started with thirty. So where is the missing dollar?