The "Monty Hall Problem" refers to a game show scenario in which you are presented with three doors to choose from, as in the famous "Let's Make a Deal" game show.

Behind one door is a car, and behind the other two there are goats.  Most people would consider the car more desirable, so that is considered the goal.

Monty Hall asks you to choose one of the three.  You do, then he eliminates one of the doors that has a goat.  Should you switch to the other door, or stick with the one you have?

Intuitively, the human mind says, well, I either have the correct door or I do not, so the chances are 50-50.  The chances are in fact 2/3 in your favor if you switch, because Monty has given you an advantage by eliminating a door after you have already chosen one.

The Perl script proves this by running the scenario a hundred thousand times and counting the results.