The 3 doors
You are in a game show. The host asks shows you 3 doors. He tells you there is $1,000,000 behind one door and in the other 2 doors there was nothing. If you pick the door with the money the. You win it. You pick a door at random. Then the host opens a door and it is empty. Then he asks you if you want to keep your door or change your mind. What should you pick?