1. Limited time only! Sign up for a free 30min personal 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!

Uniform distribution

  1. Dec 28, 2011 #1
    1. The problem statement, all variables and given/known data
    http://www.xtremepapers.com/Edexcel/Advanced%20Level/Mathematics/Subject%20Sorted/S2/S2%202008-06.pdf [Broken]

    Question 1(d)
    2. Relevant equations

    3. The attempt at a solution
    So I know this is a conditional probability question.
    Now I would have said
    P(X>8) / P(X=5)
    because it is probability I will NOT be served (i.e: time is greater than 8 mins) given I have already waited 5 mins
    this gives me infinity because x/0 = inifinty

    How do I approach this question?
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Dec 28, 2011 #2

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    No: because she has already waited 5 minutes, we know that X >= 5. You need P{X > 8}/P{X >= 5}.

    RGV
     
    Last edited by a moderator: May 5, 2017
  4. Dec 29, 2011 #3
    see thats the prob I can't see why its x≥5 because she has waited 5 mins (x=5)
    X = the amount of time Jean waits in the queue?
     
    Last edited by a moderator: Dec 29, 2011
  5. Dec 29, 2011 #4

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    X = amount of time that Jean would spend in the queue if she did not have to leave before being served; this is the random quantity representing the times she did spend in the queue on every day in the past. So, X is uniform from 0 to 10. On this one occasion we observe that after 5 minutes she is still in the queue, so on this one occasion, X >= 5. (X is not exactly equal to 5, because if it was she would not need to wait any longer; and, of course, X is not less than 5.) On this one occasion, the amount of time she spends in the queue is X (if X <= 8) and is 8 (if X > 8).
     
    Last edited by a moderator: Dec 29, 2011
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook