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Statistics: sample mean of normal distribution

  1. Oct 17, 2011 #1
    1. The problem statement, all variables and given/known data
    The diameter of a shaft in an optical storage drive is normally distributed N(μ,σ2). The drive specifies that the shaft be 0.2500 ± 0.0015 in. Suppose μ= 0.2508 in and σ = 0.0005 in. What fraction of shafts conform to the design specifications?


    3. The attempt at a solution
    I am confused with the terminology of this problem. Is 0.2500 the population mean and 0.2508 is the sample mean?
    Or is this completely unrelated, and I have to find the probability that a length be between 0.2485 and 0.2515 in?
    Some help in getting started would be appreciated.
    Thank you!
     
  2. jcsd
  3. Oct 17, 2011 #2

    Ray Vickson

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    It is crystal clear from the wording that your second interpretation is the correct one. (When I say crystal clear I mean: don't read more into the problem than what it says.)

    RGV
     
    Last edited: Oct 17, 2011
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