Customers arrive at a movie theater at the advertised movie time only to find that they have to sit through several prev

[answerhappygod]

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 five minutes. Use that as a
planning value for the standard deviation in answering the
following questions.
a. If we want to estimate the population mean time for previews
at movie theaters with a margin of error of 78 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 of error of 1 minute, what sample
size should be used? Assume 95% confidence.