Suppose we conduct a poll to estimate the proportion of vote
| Suppose we conduct a poll to estimate the proportion of voters  who favor a major presidential candidate. Assuming that 50 percent  of the electorate could be in favor of the candidate, determine the  sample size needed so that we are 95 percent confident that   | 
Solution
Note that      
       
 n = z(alpha/2)^2 p (1 - p) / E^2      
       
 where      
       
 alpha/2 =    0.025  
       
 Using a table/technology,      
       
 z(alpha/2) =    1.959963985  
       
 Also,      
       
 E =    0.01  
 p =    0.5  
       
 Thus,      
       
 n =    9603.647052  
       
 Rounding up,      
       
 n =    9604   [ANSWER]

