Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    pwsnafu

    User Avatar
    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

    HallsofIvy

    User Avatar
    Staff Emeritus
    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

    Mark44

    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook