http://en.wikipedia.org/wiki/Monty_Hall_problem This is a game about probability: Say there is three doors. Two goats and a car are hidden behind. Wanting to pick the car, you randomly picked a door. Then the game host open one of the unchoosen door which happened to contain a goat. And the host offer you a chance to switch door - to switch to the remaining unchoosen door. The question (not my question though) is, should you switch door? The correct answer is, switching is always better because the only way you could lose the game by switching is to pick the correct door at the first place, which is unlikely. But I don't understand how the probabilities transfer during the host's action. Let's say the host is going to open a door which he knows a goat is inside. To me, before the door is opened it contain some probabilities to be a car. After the door is opened, that probability is transferred away. But why the car's probability only goes to the unchoosen door instead of distributed evenly between all unopened doors?