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  1. #1
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    Is there a correct answer found in my choices. I could not find one.

    A sample of 25 is taken from a population which has a normal distribution with a mean of 60 and standard deviation of 15. The probability that the sample mean is between 55.5 and 64.5 is?

    A. .0668
    B. .2668
    C. .5468
    D. .8664
    E. .9332
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  2. #2
    hpe
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    Quote Originally Posted by NICEKID
    Is there a correct answer found in my choices. I could not find one.

    A sample of 25 is taken from a population which has a normal distribution with a mean of 60 and standard deviation of 15. The probability that the sample mean is between 55.5 and 64.5 is?

    A. .0668
    B. .2668
    C. .5468
    D. .8664
    E. .9332
    D looks right. The sample mean has standard deviation 15/sqrt(25) = 3, so 54.5 is 1.5 standard deviations below the mean and 64.5 is 1.5 standard deviations above.
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  3. #3
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    Right, you can look up z = 1.5 in a table of standard normal probabilities and find the probability in the tail is 0.668 so two tails is 0.668*2 = 0.1336, subtract from one and you get 0.8664.
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