Imagine you are on a game show and you have reached the final. You are in with the chance of winning a brand new car (something [censored] like a Corsa)

There are 3 doors. Behind one of them is the car, but behind each of the other two is a goat.

You pick a door, and to give a bit of dramatic suspense, the game show host opens one of the other doors (he knows which one the car is behind) to reveal a goat.

He then offers you the chance to change your mind and pick the other unopened door, or stick with your original choice.

What should you do to maximise your chances of winning the car?

a) stick with your origninal choice
b) change your mind and go with the other door
c) it doesn't make any difference. The odds are 50:50

What is the correct answer, and detail as simply as possible why.