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Probability of an event occurring at least once over n trials

  1. Mar 18, 2013 #1
    There is a 1 in 4 chance that on any given sexual encounter, Joe will contract an STD. If Joe has sex 4 times, what are the chances of him having an STD?
  2. jcsd
  3. Mar 18, 2013 #2


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    Science Advisor

    Hint: what is the probability of not contracting after 4 times?
  4. Mar 18, 2013 #3
    1-(.75*.75*.75*.75) = my answer?
  5. Mar 18, 2013 #4


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    Science Advisor

    Looks good.
  6. Mar 18, 2013 #5
    So how would you do it for the probability of Joe contracting an STD twice out of those 4 occasions?

    I think you would have to do a combination for this?
  7. Mar 18, 2013 #6


    Staff: Mentor

    As this is misplaced homework-type question, I am locking it. This thread was also posted in the Precalc section under Homework & Coursework.
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