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Confidence Intervals (easy question)

  1. Jul 24, 2004 #1
    Easy question but i'm being stupid somewhere. quite frustrating... enough to post it :surprise:

    Basically the question is

    Semiconductor wafer testing:
    365 dies, 201 passed probing.
    Assuming stable process calculate a 95% confidence interval for the proportion of all dies that pass the probe.

    So x_bar = 201/365
    std_dev = p*(1-p) = .228

    the answer in the book is .513,.615 and i'm not getting that. same for the next question and the one after lol.

    :yuck: :yuck:
  2. jcsd
  3. Jul 26, 2004 #2


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    Science Advisor

    The answer you say is in the book can't be right because it is not centered on the sample average: 201/365= 0.551 ((.513+ .615)/2= .564). Also your formula for standard deviation is wrong: you need a squareroot. Although I suspect it is a typo, is n 356 or 365?
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