A film alliance used a random sample of 50 U.S. citizens to estimate that the typical American spent 78 hours watching videos and DVDs last year. The standard deviation of this sample was 9 hours.
a. Develop a 95% confidence interval for the population mean number of hours spent watching videos and DVDs last year.
b. How large a sample should be used to be 90% confident the sample mean is within 1.0 hour of the population mean?