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Homework Help: Probability with Recurrence Relation

  1. Mar 26, 2009 #1
    1. The problem statement, all variables and given/known data

    Box A contains three white balls and one red ball while box B contains four white balls. One ball is randomly drawn from each box and the two balls are then randomly put back into the boxes so that each box still contains four balls. This process is performed n times. Let Pk be the probability that the red ball is in box A after the process is performed k times, where 1<=k<=n.

    (a) Find P1.
    (b) Show that Pk=3/4 Pk-1 + 1/8, where 2<=k<=n. Hence find Pk in terms of k.
    (c) Find the limit of the probability that the red ball is finally in box B as n becomes very large.
    (d) If the process is performed three times, find the probability that there are exactly two times that the red ball is in box B.

    (a) 7/8
    (b) (3/8)(3/4)k-1 + 1/2
    (c) 1/2
    (d) 57/512)

    2. Relevant equations

    Probability Formulae

    3. The attempt at a solution

    I only knew how to solve part (c) if I set Pk = Pk-1 = P when n --> infinity while

    I don't know how can I start the part (a) of this question.

    Can anyone tell me how to draw a tree diagram first?

    Thank you very much!
  2. jcsd
  3. Mar 26, 2009 #2
    The forum kept deleting my formatting so I put the tree in this picture.

    http://sites.google.com/site/blackburnt/_/rsrc/1238089640948/Home/tree.JPG [Broken]
    Does this help?
    Last edited by a moderator: May 4, 2017
  4. Mar 27, 2009 #3
    I got it!

    Thank you very much!
    Last edited by a moderator: May 4, 2017
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