First thing, I urge as many as you as possible not
to research it before having a think - try and puzzle it out yourself. Once you are thoroughly convinced that it cannot possibly be true, search for the monty hall problem on wikipedia for a nice set of explanations.
I just thought this was really interesting. Here goes:
You are on a gameshow! There are three doors, behind one of them is a car but behind the other two are goats. You must pick a door. Select 1, 2 or 3 now.
Once your selection has been made the gameshow host, who knows what is behind each door, eliminates one of the two doors that you didn't pick that doesn't
have the car. He then offers you the opportunity to change your choice.
Do you stick with your original choice, or should you switch your choice to the other door?
As I said, think it through and by all means post the conclusion you feel you come to before
you go looking it up.