A study of elephants is conducted to determine the average w

A study of elephants is conducted to determine the average weight of a certain subspecies of elephants. The standard deviation for the population is 1500 pounds. At a 95% level, how many elephants need to be weighed so the average weight will be accurate to within 250 pounds?

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 =    1500  
E = margin of error =    250  
      
Thus,      
      
n =    138.2925175  
      
Rounding up,      
      
n =    139   [ANSWER]