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Math Help - probability

  1. #1
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    Post probability

    a pair of dice is rolled together till a sum of 6 or 8 is obtained.find the probability that 6 comes before 8.
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  2. #2
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    Since 6 and 8 are equally likely on any one roll, the probability that "6 comes before an 8" (which means that the sequence of rolls terminate on a roll of 6, not 8) is exactly the same as "8 comes before a 6". Since one of those two must happen by the rules of this problem, their sum must be 1: each is equal to 1/2.
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  3. #3
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    Hello, psparmar!

    There is an "intuitive" solution for this.


    A pair of dice is rolled together till a sum of 6 or 8 is obtained.
    Find the probability that 6 comes before 8.
    We find that: . \begin{array}{ccc} P(\text{sum of 6}) &=& \frac{5}{36} \\ \\[-3mm] P(\text{sum of 8}) &=& \frac{5}{36} \end{array}

    Their probabilities are equal.
    Either event is equally likely to happen.

    Therefore, the probability that a sum of 6 precedes a sum of 8 is: . \frac{1}{2}

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