You want to estimate the mean amount of time Internet users

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 a prior Nielson survey, assume that the standard deviation of the population of monthly times spent on Facebook is 210 min. Show work, answer question, and give units

Solution

Note that      
      
n = z(alpha/2)^2 s^2 / E^2      
      
where      
      
alpha/2 = (1 - confidence level)/2 =    0.025  
      
Using a table/technology,      
      
z(alpha/2) =    1.959963985  
      
Also,      
      
s = sample standard deviation =    210  
E = margin of error =    15  
      
Thus,      
      
n =    752.9259289  
      
Rounding up,      
      
n =    753 INTERNET USERS [ANSWER]