The sample size needed to provide a margin of error of 2 or

The sample size needed to provide a margin of error of 2 or less with a .95 probability when the population standard deviation equals 11 is:

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 =    11  
E = margin of error =    2  
      
Thus,      
      
n =    116.2041293  
      
Rounding up,      
      
n =    117   [ANSWER]