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Math Help - basic probability

  1. #1
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    basic probability

    You have 130 keys and only 1 unlocks a certain door.

    What are the odds you draw that key out of a the pile of 130 on your nth try?
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  2. #2
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    Quote Originally Posted by mathman88 View Post
    You have 130 keys and only 1 unlocks a certain door.

    What are the odds you draw that key out of a the pile of 130 on your nth try?
    Draw a tree diagram. You will quickly see that Pr(N = n) = 1/130.
    Last edited by mr fantastic; February 17th 2009 at 11:10 PM. Reason: Replaced X with N
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  3. #3
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    I wrote the question down wrong... here it is corrected:

    You have 130 keys and only 1 unlocks a certain door.

    What are the odds you draw that key out of a the pile of 130 BY your nth try?
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  4. #4
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    Quote Originally Posted by mathman88 View Post
    I wrote the question down wrong... here it is corrected:

    You have 130 keys and only 1 unlocks a certain door.

    What are the odds you draw that key out of a the pile of 130 BY your nth try?
    My previous reply is relevant:

    \Pr(N \leq n) = \Pr(N = 1) + \Pr(N = 2) + .... + \Pr(N = n) = \cdot
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