3pts You want to estimate the mean amount of time Internet u

(3pts) 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]