# Question: You want to estimate the mean amount of time Internet

You want to estimate the mean amount of time Internet users spend on Facebook each month. How many Internet users must be surveyed in order to be 95% confident that your sample mean is within 15 minutes of the population mean? Based on results from prior Nielsen survey, assume that the standard deviation of the population of monthly times spent on Facebook is 210 min. What is a major obstacle to getting a good estimate of the population mean?

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