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Math Help - Tabulating probabilities of dependant r.v

  1. #1
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    Tabulating probabilities of dependant r.v

    Hi, I've got a question but before I can get going I need to tabulate the probabilities and am coming unstuck early on...

    Q:
    Finding 4 coins in his pocket, Al proposes a game of chance. He will toss all 4 coins; let X denote the number of heads obtained. Penny will then toss all the coins which came up tails when Al tossed them. Let Y denote the number of heads Penny obtains.
    What formula would I use to find the joint probability? Is it conditional as Y is dependant on X?
    Maybe someone could help with this ( for example X = 4 Tails and Y= 4 Tails or some other so I can get the idea...)
    Your help is appreciated
    Dojo

    Thanks
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    Quote Originally Posted by dojo View Post
    Hi, I've got a question but before I can get going I need to tabulate the probabilities and am coming unstuck early on...

    Q:
    Finding 4 coins in his pocket, Al proposes a game of chance. He will toss all 4 coins; let X denote the number of heads obtained. Penny will then toss all the coins which came up tails when Al tossed them. Let Y denote the number of heads Penny obtains.
    What formula would I use to find the joint probability? Is it conditional as Y is dependant on X?
    Maybe someone could help with this ( for example X = 4 Tails and Y= 4 Tails or some other so I can get the idea...)
    Your help is appreciated
    Dojo

    Thanks
    You will have a 5x5 grid with X at the top and Y on the side. Each cell in the grid is of the form (x, y). Fill in the values in each of the cells according to the rule you were given:

    "He will toss all 4 coins; let X denote the number of heads obtained. Penny will then toss all the coins which came up tails when Al tossed them. Let Y denote the number of heads Penny obtains."
    Last edited by mr fantastic; February 11th 2011 at 02:12 AM.
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  3. #3
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    I dont know what rule to use. That is the problem...

    Any more advice?
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  4. #4
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    Quote Originally Posted by dojo View Post
    I dont know what rule to use. That is the problem...

    Any more advice?
    I have told you what to do. There is no 'rule' to use. If X = 0, what are the possible values of Y? Calculate Pr(X=0, Y=0), Pr(X=0, Y=1), .... Pr(X=0, Y=4). If X = 1, what are the possible values of Y etc.

    Please show some effort.
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