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Math Help - probability: rolling a die

  1. #1
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    Red face probability: rolling a die

    p = 1/6
    you roll a die and wait for the number 5 on the die.
    Last edited by shirel; August 28th 2007 at 01:11 AM.
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  2. #2
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    Quote Originally Posted by shirel View Post
    exercise:

    p = 1/6
    you roll a die and wait for the number 5 on the die.

    what outcome is to be expected here? why?

    or if you can't answer the question: what can't be expected?


    help me
    Instead consider what is the probability of NOT getting a 5. It is 5/6 if you do that n times you have (5/6)^n.

    Hence, the probability of getting at least one 5 is 1-(5/6)^n
    We want this to be expected, i.e,
    1-(5/6)^n >= 1/2
    Thus,
    (5/6)^n <= 1/2
    Find the first value of n which makes this true.
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