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Homework Help: Statistics: Using a PDF function

  1. May 5, 2012 #1
    1. The problem statement, all variables and given/known data
    I am doing a practice final exam in preparation of my actual final exam next week. Here is the link. I am doing problem number 2.

    http://www.math.stevens.edu/~ifloresc/Teaching/2011-2012/MA222S12/Final_Exam_Summer2011.pdf

    3. The attempt at a solution

    So this seems pretty straight forward starting out, but I noticed that the PDF does not integrate to 1 as it should. So I redefined the function so that it does. Was this the correct thing to do? Because later in the problem I have more issues with finding the standard deviation. It appears as though I get a negative variance! Here is my work..

    http://img43.imageshack.us/img43/9818/work1hm.jpg [Broken]

    If anyone could help me I would be so thankful!
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. May 5, 2012 #2

    Ray Vickson

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    Science Advisor
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    Question 2 has a serious typo. The function f(x) as described goes negative for x > 1/2, so cannot possibly be a legitimate pdf.

    RGV
     
    Last edited by a moderator: May 6, 2017
  4. May 5, 2012 #3
    Thats what I thought! But I wasn't sure! I hope to god he didn't ACTUALLY give this PDF in a final.
     
  5. May 5, 2012 #4
    Since I already posted the questions, I REALLY do not understand number 6. They didn't give the number of n, so how can I find the expected value when n is large??
     
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