a marketing firm wants to estimate how much root beer the av

a marketing firm wants to estimate how much root beer the average teenager drinks per year. a previous study found a standard deviation of 1.12 liters. how many teenagers must the firm interview in order to have a margin of error of at most .1 liter when constructing a 99% confidence interval?

a.29

b.832.39

c.833

D.832

Solution

Note that      
      
n = z(alpha/2)^2 s^2 / E^2      
      
where      
      
alpha/2 = (1 - confidence level)/2 =    0.005  
      
Using a table/technology,      
      
z(alpha/2) =    2.575829304  
      
Also,      
      
s = sample standard deviation =    1.12  
E = margin of error =    0.1  
      
Thus,      
      
n =    832.2814296  
      
Rounding up,      
      
n =    833   [ANSWER, C]