The Monty Hall Problem is a statistics problem that can be solved using your A-Level Maths knowledge of probability trees, but that didn't stop it being the subject of much debate amongst some very clever mathematicians. Even now, not everyone agrees on the answer...
You're on a game show where you can win a car, or one of two goats. The car and goats are hidden behind a door each. You select a door from one of the three. The game show host, who knows what is behind every door opens one of the unpicked doors to reveal a goat. The host gives you the choice of sticking with the door you have already picked, or swapping to the other remaining open door.
What should you do to stand the best possible chance of winning the car?