Monty Hall

So I just got a book called Einstein's Riddle by Jeremy Stangroom. It is filled with paradoxes, riddles and such. I attempted the actual Einstein's Riddle, though I must admit that I failed to come up with the correct problem. Then I came across my favorite probability problem of all time: The Monty Hall Problem.

It goes like this: You are a contestant on a gameshow with three doors to choose from. Behind one door is a Ferrari, but behind the other two are goats. So you pick your door, it doesn't matter which. Since Monty knows which item is behind what door, he then opens one of the other doors to reveal a goat. He then gives you the option of switching your choice the remaining unopened door. Should you?

I recall first hearing about this problem in the movie 21, about the MIT kids who go to Las Vegas to make money card counting. The explanation they gave made no sense to me, but luckily, this book's explanation did. If you don't know/can't figure out the answer, then you should go look it up. Trust me, it isn't what you think.