Question

A brand of power supply has a labeled voltage as 12 V . A quality control group randomly sampled 15 units of such power supplies and measure their real output voltage levels. Suppose these measurements follow a normal distribution. The sample yields a mean output of 12.4 V with a standard deviation of 0.5.

(a) Provide a 95% confidence interval for the true mean voltage µ.

(b)Suppose that controlling the variability in the output voltage of these power supplies is also of interest to the manufacturer. Construct a 95% 1-sided confidence upper bound for the true variance of the output.

(c)Suppose the confidence interval for µ in part (a) is not narrow enough and a second study is planned. Determine the sample size, n, of this new study such that the 95% 2-sided confidence interval will have a width of 0.2 V

Answer 1