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Two Stats questions for Math nerds (std. deviation, mean, subsets)

  1. Oct 12, 2004 #1

    ski

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    1. If a school offers 3200 separate courses and a survey of these courses determines that the class size is 50 with a standard deviation of 2, what would one expect for the average and standard deviation of a subset of 50 of these classes selected randomly?

    2. In a survey to estimate the average size (number of students) of a class at a university, ten courses are picked at random and the class size of each is determined. The result is 48 students in a class with a standard deviation of 12 students. Assuming that the sample of 10 classes is representative subset of the whole and that class size is a Gaussian random variable, what would one expect the average and standard deviation to be for samples of 40 classes and 160 classes?

    It's been so long since I've taken stats... REALLY long :confused: Any help on one or botha these would help me this week :smile:
     
  2. jcsd
  3. Oct 13, 2004 #2

    ski

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    Here was what's suggested I do:

    1.We'd expect an average of 50+- 1.98*2/sqrt(50)
    The standard deviation by definition is 2/sqrt(50)

    2. Not as sure about this one but following the logic of the last one..
    sqrt(10)*12=s
    and then stdv= s/sqrt(40)
    and s/sqrt(160)
    where the mean = STDV*2.021,STDV*1.97 respectively



    Is the first solution really that easy?
     
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