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Math Help - Sample mean

  1. #1
    Newbie
    Joined
    Apr 2005
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    2

    Sample mean

    A new paper calls 20 of its subscribers to determine their mean income. The distribution of the sample mean is:

    a. unknown
    b. binomial
    c. normal
    d. approximately normal


    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


    Decreasing the sample size:

    a. decrease the sample mean
    b. decrease the standard deviation of the sample mean
    c. increase the standard deviation of the sample mean
    d. increase the sample mean
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  2. #2
    Newbie
    Joined
    Apr 2005
    Posts
    8

    I know an answer

    the answer to your third problem is: c
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