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Find the 90% two-sided confidence interval for the mean score.

  1. Mar 14, 2014 #1
    The distribution of grades is know to follow a normal distribution, but the mean and variance are unknown. A random sample of 12 students produced the following scores:

    59, 84, 68, 93, 49, 77, 82, 75, 81, 58, 70, 80

    Find the 90% two-sided confidence interval for the mean score.
     
  2. jcsd
  3. Mar 15, 2014 #2

    Stephen Tashi

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    Does this grading system allow negative grades? If not, the the grades can't actually be normally distributed.

    Of course, perhaps this is a homework problem where such technicalities are ignored. If so, you should post it somewhere in the "Homework & Coursework Questions" section of the forum and show your attempt at solution.
     
  4. Mar 15, 2014 #3

    statdad

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    "Does this grading system allow negative grades? If not, the the grades can't actually be normally distributed."

    Nothing is ever really normally distributed: if the standard deviation is small enough then to a very good approximation the normal distribution can be quite useful.
     
  5. Mar 17, 2014 #4

    DrDu

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    You might consider a Student's t-distribution
     
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