1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    phinds

    User Avatar
    Gold Member
    2016 Award

    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

    pasmith

    User Avatar
    Homework Helper

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

    phinds

    User Avatar
    Gold Member
    2016 Award

    Ah ... isn't that what I just said?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted