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Probability confusion

  1. Oct 7, 2013 #1
    The problem statement, all variables and given/known data
    How many times do we need to roll a fair die to get a better than evens chance of at least one six?

    The attempt at a solution
    Let n be the number of rolls. Am I trying to find how large n must be so P(At least one six)≥ 1/2?
    I'm working on the basis that I need to solve the probability of the union of events Ai, where Ai denotes the event of rolling i sixes, i =1,2,3...., being greater than 1/2.
    Any help or nudge in the right direction will be appreciated.
  2. jcsd
  3. Oct 7, 2013 #2


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    Gold Member

    I'd attack it by finding the odds of NOT getting a six with one roll, then 2 rolls, then 3 rolls, and so on. As soon as that probability drops below 50% you've got the answer.
  4. Oct 7, 2013 #3


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    Homework Helper

    P(at least one six) = 1 - P(no sixes)
  5. Oct 7, 2013 #4


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    Gold Member

    Ah ... isn't that what I just said?
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