A game-show host has a car behind 1 of 3 doors There's a goat behind other doors You point to door 1 The host shows you that door 3 has a goat What should you do- switch stay doesn't matter?

This is the well known Monty Hall problem, named after the presenter of a TV game show which presented players with this dilemma. For a good explanation of the background and winning strategy, see the Wikipedia: Monty Hall problem at: http://en.wikipedia.org/wiki/Monty_Hall_problem