A researcher is interested in determining the average number

A researcher is interested in determining the average number of years employees of a company stay with the company. If past information shows a standard deviation of 7 months, what size sample should be taken to that at a 95% confidence the sampling error will be 2 months or less?

Solution

Note that  
  
n = z(alpha/2)^2 s^2 / E^2  
  
where  
  
alpha/2 =    0.025
  
Using a table/technology,  
  
z(alpha/2) =    1.959963985
  
Also,  
  
s = sample standard deviation =    7
E = margin of error =    2
  
Thus,  
  
n =    47.05787055
  
Rounding up,  
  
n =    48 [ANSWER]