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Question about the movie 21

Discussion in 'Anything goes' started by Simon_Cowbell, Aug 21, 2008.

  1. Simon_Cowbell

    Simon_Cowbell Active Member

    The first time we see Sturgess and Spacey, Spacey poses a gameshow question.

    There are three doors, two with a goat behind them and one with a car.

    Initially Ben picks door one ... 33.3 percent chance for each door.

    Then, Spacey says that Door 3 is revealed to have a goat.

    Next thing we see, Ben has switched his pick to door 2, saying the odds are 66.7 percent. Huh?

    Did anyone see this scene? What am I missing?
     
  2. slappy4428

    slappy4428 Active Member

    Ask 21. She's the one hanging with a goat.
     
  3. Walter_Sobchak

    Walter_Sobchak Active Member

  4. Simon_Cowbell

    Simon_Cowbell Active Member

    Wow..... I do NOT get that.

    And I scored 1300 on my math SAT. No genius, but no rube, either.

    Whew.
     
  5. slappy4428

    slappy4428 Active Member

    which dont you get? Monty Hall picking the right door or 21 being able to tell you about picking the right goat?
     
  6. Simon_Cowbell

    Simon_Cowbell Active Member

    You have a 50 percent chance of guessing right, I think.
     
  7. Piotr Rasputin

    Piotr Rasputin New Member

    Did you take it in an era when top score for math wasn't 800?

    (seriously; I don't know).

    And . . . I can't wrap my head around the solution to that problem. Seems switching should logically mean nothing. Knowing what's behind one of the doors shouldn't change your answer, unless you originally chose No. 3.

    But this is like "Deal or No deal," where I've had people tell me "It's all about probabilities," while I think it looks a hell of a lot like luck.
     
  8. Wenders

    Wenders Active Member

    Suddenly, I don't feel so retarded for not knowing the answer to that problem. I don't claim to understand math most of the time (I was moderately good at algebra but when it came to geometry, it was game over). It makes absolutely NO sense to me. I would think it would be a 50/50 chance of getting the right door after they revealed the goat. Even after reading the Wikipedia entry, I still don't understand.

    ....and this is why I have a B.A. in journalism. The last math class I took was five years ago.
     
  9. CentralIllinoisan

    CentralIllinoisan Active Member

    Think of it this way ... You have 100 doors, 99 of which have goats behind them. One has a car.

    You pick one, say, No. 10. You have a 1 percent chance of picking the car.

    Then, the host -- leaving No. 10 closed -- reveals goats in 98 other doors.

    So only two doors remain closed: your No. 10 and another, random door.

    Do you switch? Of course you do. The odds of you having selected the correct door to begin with were against you -- 99 percent against you in my example and 66 percent against you in the three-door example.

    If the odds were AGAINST you making the correct decison the first time, then when you reverse it, that decision is in your FAVOR.
     
  10. buckweaver

    buckweaver Active Member

    Bingo. Those two grafs, especially that last sentence, sum it up better than that entire Wiki article.
     
  11. Simon_Cowbell

    Simon_Cowbell Active Member

    I was wholly stunned by the movie and wikipedia entry.

    680 math.
     
  12. Piotr Rasputin

    Piotr Rasputin New Member

    That defies logic, and is counterintuitive.

    Mathmeticians have way too much time on their hands.
     
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