The widths of 100 elevator rails have been measured. The sample mean and standard deviation of the elevator rails are 2.05 inches and 0.01 inch.
a. Find a 95% confidence interval for the average width of an elevator rail. Do you need to assume that the widths of elevator rails are normally distributed?
b. How large a sample of elevator rails would you have to measure to ensure that you could estimate, with 95% confidence, the average diameter of an elevator rail within 0.01 inch?