A researcher is interested in evaluating a certain brand of radial auto tire. Twenty tires are randomly selected from retail outlets throughout the country and each is placed on a special machine that rotates the tires at a constant speed (equivalent to 55 miles per hour) against the friction equivalent of a 4,000 pound auto being driven on a smooth highway. Each tire is run until there is no tread left. The number of miles (in thousands) were as follows: 40, 30, 32, 35, 39, 35, 31, 36, 37, 35, 34, 35, 37, 34, 36, 38, 35, 36, 35, 36.

Required:
Estimate the population mean within a confidence interval of 0.95.