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Simplifying the Conditional probability

  1. Sep 7, 2012 #1
    P(S1 [itex]\cap[/itex] S2 [itex]\cap[/itex] S3 | r)
    How do I simplfy the above equation if S2 and S3 are independent of r ?
  2. jcsd
  3. Sep 7, 2012 #2

    Stephen Tashi

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    Science Advisor

    I've don't recall seeing a book that gives the probability law
    [itex] P((X|Y)|Z) = P(X | (Y \cap Z) ) [/itex]
    but I think its true. How to argue it depends on whether you are approaching probability as measure theory or something simpler.

    You can also apply the usual probability laws with a condition lilke "[itex]| Z[/itex]" tagged onto every term. For example,
    [itex] P(A \cap B) = P(A|B) P(B) [/itex]
    [itex] P(A \cap B | Z) = P( (A|B)|Z) P(B | Z) [/itex]

    See if you can make progress by applying those ideas.
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