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Homework Help: P(X=i) from given PGF

  1. Dec 11, 2005 #1
    Hi people, I was wondering if anyone could give me a hint with this problem.
    A RV X has PGF Gx(s)= (4-s)/3(4-3s)

    I need to get the P(X=i) from here. I know i can manipulate the above to get the sum to infinity of a geometric series, but i end up with the term
    (4-s) still in the P(X=i) which i dont think can be right. Anybody got any hints on how to rearrange the above so as to eliminate the s in the numerator so I can obtain P(X=i)? Thanks a lot, Jack
     
  2. jcsd
  3. Dec 11, 2005 #2

    matt grime

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    multiply out the (4-s) and the infinte series.
     
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