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Math Help - Probability of rolling 2 dice

  1. #1
    rmn
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    Question Probability of rolling 2 dice

    Ok so there is this question I have been working on for over 2 hours including reading the whole chapter and going through my notes but it doesn't really sseem to make sense to me:
    http://i207.photobucket.com/albums/b.../questiona.jpg
    http://i207.photobucket.com/albums/b.../questionb.jpg

    This is what i've done so far:
    So P(B and D) I have 6/18 because thats how much of B there is in D right? or is it P(B) multiply P(D)? but still I don't understand when it asks P(B and D) = P(B) because isn't P(B) just 6/36? which isn't the same as 6/18?

    If anyone could help me please
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by rmn View Post
    Ok so there is this question I have been working on for over 2 hours including reading the whole chapter and going through my notes but it doesn't really sseem to make sense to me:
    http://i207.photobucket.com/albums/b.../questiona.jpg
    B denote the event of a sum of 7 on the two die, and D the event that the
    sum of the two die is odd.

    If B has occured then of necessity so has D as 7 is odd.

    The even (B and D) means both events have occured, which always has the
    same truth value as B, so in this case:

    P(B and D)=P(B)

    Alternativly draw a Venn diagam, then B is entirly enclosed withing D, and
    the event (B and D) is represented by the area of overlap of B and D, which
    in such a case is B.

    Drawing a Venn diagram will also show why P(B or D)=P(D) when B is contained in
    D.

    RonL
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