A marketing firm wants to estimate the average amount spent by patients at the hospital pharmacy. For a sample of 70 randomly selected patients, the mean amount spent was $55.50 and the standard deviation was $7.75.
(a) Find a 90% confidence interval for the mean amount spent by patients at the pharmacy. Show your calculations and/or explain the process used to obtain the interval.
(b) Interpret this confidence interval and write a sentence that explains it.