Refer to Exercise 9.41. Construct a 95% confidence interval for the true standard deviation of the thickness of sheets produced on this shift.

Data from in Exercise 9.41

Plastic sheets produced by a machine are periodically monitored for possible fluctuations in thickness. Uncontrollable heterogeneity in the viscosity of the liquid mold makes some variation in thickness measurements unavoidable. However, if the true standard deviation of thickness exceeds 1.5 millimeters, there is cause to be concerned about the product quality. Thickness measurements (in millimeters) of 10 specimens produced on a particular shift resulted in the following data.
Do the data substantiate the suspicion that the process variability exceeded the stated level on this particular shift?

(Test at a = .05.) State the assumption you make about the population distribution .

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