It seems that, with two doors closed, everything comes down to fifty-fifty. However, the odds are not equal: the way the presenter chooses which door to open changes everything.
The Monty Hall Problem
Riddle statement
In a contest there are three doors. Behind one there is a car and behind the other two there are goats. You choose a door. The presenter, who knows where the car is, always opens one of the other two doors that a goat has, never opens your door and always offers you to change to the only door that is closed.
If you decide to change doors, does your probability of winning the car improve? What is that probability?