In order to estimate the mean amount of time computer users spend on the internet each month, how many computer users must be surveyed in order to be 90% confident that your sample mean is within 12 minutes of the population mean?
Assume that the standard deviation of the population of monthly time spent on the internet is 191 min.
What is a major obstacle to getting a good estimate of the population mean? Use technology to find the estimated minimum required sample size.