Say you are on a game show [historical sidenote: this question was first played on the 60s American game show Let’s Make a Deal, hosted by Monty Hall], and there are three closed doors. Behind one door is a car, the prize you dream of, and behind the other two are goats. You pick a door. The host, who knows what’s behind each door, opens another which reveals a goat. Now, the host lets you make another choice: should you stick with you first door choice, or should you switch and pick a different door, in order to win the car?
(Hint: this is a conditional probability problem)