Question

An automobile manufacturer would like to know what proportion of its customers are dissatisfied with the service received from their local dealer. The customer relations department will survey a random sample of customers and compute a 95% confidence interval for the proportion that are dissatisfied. From past studies, it believes that this proportion will be about 0.3. Find the sample size needed if the margin of error of the confidence interval is to be no more than 0.045. (Round your answer up to the next whole number.)

( _______ ) customers

Answer 1

Preliminary estimate for proportion (Known) =    0.3
Margin of error =E=0.045
Level of significance =   1-0.95=0.05
Z critical value is (by using Z table) =1.96
Sample size formula is                   


=398.37                  
                  
Therefore, sample size approximately will be 399