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Math Help - Finding mean, variance and standard deviation.

  1. #1
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    Finding mean, variance and standard deviation.

    If anyone could help me out with the following questions, that would be great!

    1. In an exam, 95% of the scores are between 48 and 80. What are the mean and variance of scores?

    2. There is a binomial distribution where n=20 and p=10q. What is the mean and standard deviation?
    Last edited by mr fantastic; September 4th 2011 at 07:34 PM. Reason: Re-titled.
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  2. #2
    Grand Panjandrum
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    Re: Probability Question

    Quote Originally Posted by gbooker View Post
    If anyone could help me out with the following questions, that would be great!

    1. In an exam, 95% of the scores are between 48 and 80. What are the mean and variance of scores?
    Impossible to answer with out the missing information about what you are to assume about the distribution of marks.

    If we assume this is a symmetric 95% interval [48,80] are the mean +/- 1.96 standard deviations. You are expected to know that the standard deviation is the square root of variance.

    CB
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  3. #3
    Grand Panjandrum
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    Re: Probability Question

    Quote Originally Posted by gbooker View Post
    2. There is a binomial distribution where n=20 and p=10q. What is the mean and standard deviation?
    If p=10q then as p+q=1 we have p=10/11 and q=1/11.

    Mean is np, and standard deviation is \sqrt{npq}
    CB
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