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Math Help - Question on Normal Distribution

  1. #1
    Junior Member asemh's Avatar
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    Question on Normal Distribution

    Hey,
    Im having trouble with this question, i really dont know how to start it...

    Calculate the probability that 200 rolls of two dice rolls will unclude

    a) more than 30 sums of 5
    b) between 30 and 40, inclusive, sums of 5

    Thanks in advance.
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  2. #2
    Master Of Puppets
    pickslides's Avatar
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    Are you sure this is normal? I am thinking it is a normal approximation to binomial.

    Anyhow, first find the probability of the die summing to 5 on any given roll.

    What do you get?
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  3. #3
    Junior Member asemh's Avatar
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    Yea sorry i meant Normal approximation =\

    ooh nvm i got it

    This is what i did.. found that the probability of getting 5 from two dice is 1/9

    then i found the mean (1/9 * 200) = 22.22
    standard deviation = 4.44

    and then i did P(x>30.5)
    and i got the right answer which is 0.0312

    Thanks for your help.
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  4. #4
    Master Of Puppets
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    Well maybe try something like P(X\geq 30 ) = P\left(Z\geq \frac{30 - np}{\sqrt{np(1-p)}}\right)

    Now can you find n and p ??
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