This is a little maths/ probability challenge I like- the obvious answer is not the right one
You are in a game show. There are three doors. Behind 1 door is a car, behind the other two is nothing.
The game show host knows what is behind each door. He asks you to pick a door. You do. He then looks at the two doors left, and opens one to reveal nothing behind it (he knew this would happen).
There are now two doors remaining. The door you picked (that hasn't been opened) and the other door.
He says to you, "Now, would you like to stick to your original choice, or change to the other unopened door?"
Is your probability of winning greater if you stick with your original choice, or change to the other remaining door?