Math Puzzle

[Poosc]

Right ok imagine you are are one of those shows on tv and you have the chance to win some money. There are three doors and behind one is a stack load of cash.
_____ _____ _____
|.........|..........|........|
|....1...|....2....|...3....|
|.........|..........|........|

The presenter asks you to pick a door. You don't open it! (The presenter knows which door the cash is behind.) He then picks another door and opens it. There's nothing inside....

NOW the question is should you stay with your choice or pick the other door.
(its pretty basic maths on probability but don't be fooled its not THAT easy!)
Have fun

[nefeltari]

First there's 33% to pick the right one, then you're sure that's nothing in 1/3 = Then there's 50%, so it's no deal if u pick a new one or u stcik with your choice, or am I getting this wrong? xD

[Poosc]

hmm that sounds like its right but that wasnt what i got told today

[XplittR]

Well, the presenter of course want the money himself, so why should he pick a door that there is not gold in? Therefore bigger probability for taking the door you already have taken

[Poosc]

lol that makes sense but really all he is doing is eliminating one door. Even when i got told the solution to this i didnt believe him!! Supposedly when this was posted a load of PHD students believed that it wasnt correct but supposedly it is! :S!!!

[Serverman]

Arrrgh!!! I should pay attension in class >.< WE HAD THIS RIDDLE!!!! ARGHHH!!!! *hits head* STUPID ME!!! :O (Get out my math book ) Nope not there either... Well... ill have a try
Since when you choose a door, one gets opened, and then there is a 50% chance of choosing right, while at the start its just 33%chance, so you should pick the other door i think XD

[Poosc]

you're pretty close tempted to give it to ya really! your answer is right! its just the reason which is SLIGHTLY off!

[Serverman]

Did i miscalculate or is it 50%?
Edit: [12-02, 22:44] Serverman Because you had a 30%chance to get it right, and then when he removed one you got a 70% chance, ya?
[12-02, 22:43] Serverman Its like 70% is it not?
Copyed outta ChatBox cuz im too lazy to type it again Now im off to bed Nighty!!