Customers arrive at the movie theater at the movie time indicated only to find they need to sit through commercials and previews. Many complain that this time is too long. WSJ 2012
determined in a preliminary sample that the standard deviation of the amount of time devoted to
previews is 4 minutes. If we want to estimate the population mean time for previews at movie
theatres with a margin of error of 75 seconds, what sample size should be drawn?
b. Assume a 99% confidence level

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