An article in the National Geographic News ("U.S. Racking Up Huge Sleep Debt," February 24, 2005) argues that Americans are increasingly skimping on their sleep. A researcher in a small Midwestern town wants to estimate the mean weekday sleep time of its adult residents. He takes a random sample of 80 adult residents and records their weekday mean sleep time as 6.4 hours and standard deviation is fairly stable at 1.8 hours.
a. Calculate the 95% confidence interval for the population mean weekday sleep time of all adult residents of this Midwestern town