Passenger comfort is affected by the amount of pressurization in an airline cabin. Higher pressurization permits a closer-to-normal environment and a more relaxed flight. A study by an airline user group recorded the corresponding air pressure on 30 randomly chosen flights. The study revealed a mean equivalent pressure of 8,000 feet with a standard deviation of 300 feet.
a. Develop a 99% confidence interval for the population mean equivalent pressure.
b. How large a sample is needed to find the population mean within 25 feet at 95% confidence?