I'm being lazy - another brainteaser:
You are on a game show and win! The host gives you a choice of 3 doors, A, B and C. Behind one is the prize* and there is nothing behind the other two.
He asks you to choose a door. You choose one (let’s say B).
He then opens one of the other doors that (he knows) doesn’t have the prize (say A).
You are now offered the chance of staying with the first door you chose (B), or changing to the one remaining door (C).
Q: What should you do? Or does it make no difference?
*Feel free to imagine whatever prize you like. You aren't really on a game show after all, it's just made up. I'm imagining some kind of "marker-bot". A robot that could do all my marking for me.