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Homework Help: Probability and Statistics (Check my answer)

  1. Aug 20, 2006 #1
    Hi guys, i was given the following problem:

    The mean diameter of a batch of bolts is 9.711mm and the standard deviation of the batch is 0.126mm

    The tolerance for this batch of components is 9.73mm to 9.97mm.
    In a batch of 2000 bolts, determine the following:

    a) The percentage of bolts rejected assuming the bolts are normally distributed.

    My answer:

    (9.97 - 9.73) / 0.126 = 1.90

    1.90 Corresponds to: 0.9713

    1 - 0.9713 = 0.0287

    (Little less than 3% are rejected)

    0.0287 x 2000 = 57.4

    = 57 rejected out of 2000

    Can anybody tell me if i'm right?
  2. jcsd
  3. Aug 20, 2006 #2


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    Science Advisor

    No, your first step is not right. But I'm not sure you have written down the problem correctly. If the mean is 9.711, you would expect the tolerated values to go from somewhere below 9.711 to somewhere above it, not from 9.73 to 9.97. Did you mean that the mean is 9.811?
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