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Conditional Probability for discrete random variables.

  1. Apr 24, 2012 #1
    1. The problem statement, all variables and given/known data
    Compute P(X=k l X+Y=p)

    2. Relevant equations

    3. The attempt at a solution

    No idea. Kind of understand page #1. Although it seems like there's a lot of unnecessary stuff. Could have gone straight from the top to the bottom. And I don't know why/if you even have to substitute the X+Y=p for Y=k-p. Totally lost on page 2. No idea whats going on there. Says it's being split up because it's independent, but no idea where the 1/3 and 2/3 for 0 and 1 come form. Let alone the rest of page 2. :uhh:
    So, in short: What's exactly step 1,2,3 etc. ?

    Attached Files:

  2. jcsd
  3. Apr 24, 2012 #2

    Ray Vickson

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    The 1/3 and 2/3 for 0 and 1, etc., are just examples, so the writer has some definite numbers to work with when practicing use of the formulas.

  4. Apr 25, 2012 #3
    I'm also trying to solve this similar problem, and also have no idea how to go about solving it.
  5. Apr 25, 2012 #4

    Ray Vickson

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    For two events A and B we have
    [tex]P(A|B) = \frac{P(A \cap B)}{P(B)}.[/tex]

    That's all there is to it. Just figure out what are the events A and B in your problem.

    Last edited: Apr 25, 2012
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