Customers arrive at a movie theater at the advertised movie time only to find that they have to
sit through several previews and prepreview ads before the movie starts. Many complain that the
time devoted to previews is too long..A preliminary sample conducted by The Wall Street Journal
showed that the standard deviation of the amount of time devoted to previews was 4 minutes.
Use that as a planning value for the standard deviation in answering the following questions.
Round your answer to next whole number.
a. If we want to estimate the population mean time for previews at movie theaters with
a margin
of error of 75 seconds, what sample size should be used? Assume 95% confidence.
b. If we want to estimate the population mean time for previews at movie theaters with a margin a
of error of 1 minute, what sample size should be used? Assume 95% confidence.