Twenty-one warranty repairs were selected from a population of 126 by selecting every sixth item. The population consisted of "loose, not attached" minivan electrical wires (one of several electrical failure categories the dealership mechanic can select). The mean repair cost was $45.664 with a standard deviation of $27.793.
(a) Construct a 95 percent confidence interval for the true mean repair cost.
(b) What sample size would be needed to obtain an error of 6$5 with 95 percent confidence?
(c) Construct a 95 percent confidence interval for the true standard deviation. (Data are from a project by MBA student Tim Polulak.)