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 mm, there is cause to be concerned about the product quality.Thickness measurements (in millimeters) of 10 specimens produced on a particular shift are as follows:

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Construct a 95% confidence interval for the true standard deviation of the thickness of sheets produced on this shift.(Note:from the sample data, s = 2.2706).