A jar of peanuts is supposed to have 16 ounces of peanuts. The filling machine inevitably experiences fluctuations in filling, so a quality-control manager randomly samples 12 jars of peanuts from the storage facility and measures their contents. She obtains the following data:

(a) Verify that the data are normally distributed by constructing a normal probability plot.
(b) Determine the sample standard deviation.
(c) Construct a 90% confidence interval for the population standard deviation of the number of ounces of peanuts?

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15.94 15.36 15.84 15.84 15.74 16.21 15.52 16.16 15.78 15.51 16.28 16.53