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Math Help - Tree/Permutation - Urn problem

  1. #1
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    Tree/Permutation - Urn problem

    An urn contain one white, two red, and two blue marbles. A game is played by selecting marbles until the white one is selected. How many outcomes does this game have?

    I got 65, but apparently it's wrong.

    My reasoning, Red had 16 outcomes.

    16 (red 1)+16 (red 2)+16 (blue 1)+16 (blue 2) +1 (white)=65
    Last edited by Sakurazaki; September 25th 2009 at 04:48 PM.
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  2. #2
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    Quote Originally Posted by Sakurazaki View Post
    An urn contain one white, two red, and two blue marbles. A game is played by selecting marbles until the white one is selected. How many outcomes does this game have?
    This is an absolutely poorly worded problem. There are two readings.
    If we select a ball and then discard it, then there are at most six ways for this to be done.

    If we select a ball and then return it, then there are infinitely many ways this to be done.
    There is no reason that a white ball is ever selected.
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  3. #3
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    It is we select a ball and then discard it. But I tried inputing six and it still says it's wrong.
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  4. #4
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    Hello Sakurazaki
    Quote Originally Posted by Sakurazaki View Post
    An urn contain one white, two red, and two blue marbles. A game is played by selecting marbles until the white one is selected. How many outcomes does this game have?

    I got 65, but apparently it's wrong.

    My reasoning, Red had 16 outcomes.

    16 (red 1)+16 (red 2)+16 (blue 1)+16 (blue 2) +1 (white)=65
    It doesn't take long to list all the possibilities. Here they are:

    W
    RW
    BW
    RRW
    RBW
    BRW
    BBW
    RRBW
    RBRW
    BRRW
    RBBW
    BRBW
    BBRW
    RRBBW
    RBRBW
    RBBRW
    BRRBW
    BRBRW
    BBRRW


    So I reckon the answer is 19

    Grandad
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  5. #5
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    Aha! Thanks, I figured out what I did wrong. I wasn't supposed to get that many answers in the first place.
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