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 90% confident that your sample mean is within 14 minutes of the population mean? Assume that the standard deviation of the population of monthly time spent on the internet is 200 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 nothing computer users. (Round up to the nearest whole number.) What is a major obstacle to getting a good estimate of the population mean?

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

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

C. There may not be 553 computer users to survey.

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 =    0.05  
      
Using a table/technology,      
      
z(alpha/2) =    1.644853627  
      
Also,      
      
s = sample standard deviation =    200  
E = margin of error =    14  
      
Thus,      
      
n =    552.1517253  
      
Rounding up,      
      
n =    553   [ANSWER, MINIMUM SAMPLE SIZE]

***********************

b)

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