In order to estimate the mean amount of time computer users

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 95% confident that your sample mean is within 15 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.

The minimum sample size required is­­­______ computer users?

What is a major obstacle to getting a good estimate of the population mean?

A - There may not be 623 computer users to survey.

B - It is difficult to precisely measure the amount of time spent on the internet, invalidating some data values.

C - The data does not provide information on what the computer users did while on the internet.

D - There are no obstacles to getting a good esitmate of the population mean.

Solution

a)

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 =    191  
E = margin of error =    15  
      
Thus,      
      
n =    622.8455966  
      
Rounding up,      
      
n =    623   [ANSWER]

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b)

B - It is difficult to precisely measure the amount of time spent on the internet, invalidating some data values. [ANSWER]