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Math Help - Probability

  1. #1
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    Mar 2009
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    Probability

    Hello All,
    I was asked by a colleague to work out some probabilities (its been a good 20+ years since I have done any real probabilities mind), and I have worked out some but I know they are wrong I just can't fathom why.

    We have X Dice, with Y Sides, and its possible two or more sides can have the the symbol (so these dice aren't simple 1-6 D6's).
    So for example
    Dice 1 (D8) = A A B B B C D

    I need to work out combination of using multiple dice from various symbol layouts can effect the results of getting a "A" for example or getting two "A"'s.
    Not to bad, the problem is if some dice "negate" other results, i.e.

    Dice A (D8) = -A -A -AA B B B C D
    As in two sides negate an A and one side negates one or two A's.

    This is where my probabilities skills have become to rusty for me to work out, help would be much appreciated! (especially as we are dealing up with pools of 20+ dice with various (6+) variations on symbols)

    Ta!
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  2. #2
    Junior Member
    Joined
    Jan 2009
    Posts
    44
    Quote Originally Posted by pauljh View Post
    Hello All,
    I was asked by a colleague to work out some probabilities (its been a good 20+ years since I have done any real probabilities mind), and I have worked out some but I know they are wrong I just can't fathom why.

    We have X Dice, with Y Sides, and its possible two or more sides can have the the symbol (so these dice aren't simple 1-6 D6's).
    So for example
    Dice 1 (D8) = A A B B B C D

    I need to work out combination of using multiple dice from various symbol layouts can effect the results of getting a "A" for example or getting two "A"'s.
    Not to bad, the problem is if some dice "negate" other results, i.e.

    Dice A (D8) = -A -A -AA B B B C D
    As in two sides negate an A and one side negates one or two A's.

    This is where my probabilities skills have become to rusty for me to work out, help would be much appreciated! (especially as we are dealing up with pools of 20+ dice with various (6+) variations on symbols)

    Ta!
    What game are you playing? Are you trying to calculate your odds of winning?

    You're example of Dice 1 has eight sides so the probability of;

    Ap = \frac 28

    Ap = \frac 14

    Bp = \frac 38

    Cp = \frac 18

    Dp = \frac 18

    If you role the dice three times, you multiple the probabilities together ie

    probability of rolling A,A,B in 3 dice is

     Ap^2 * Bp

    If you now have a side which is AA and this negates the effect of rolling an A ie you roll 3 dice AA,A,B then only the B is used then you use the same formula;


    AAp = \frac 18

    Ap = \frac 18

    Bp = \frac 38

    Cp = \frac 18

    Dp = \frac 18


    probability of rolling AA,A,B in 3 dice is

     AAp * Ap * Bp

    Does this help? What combinations are you attempting to calculate? A little more detail and I could help you build an excel spreadsheet to work everything out.
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