Question

The water works commission needs to know the mean household usage of water by the residents of a small town in gallons per day. They would like the estimate to have a maximum error of 0.140.14 gallons. A previous study found that for an average family the variance is 1.691.69 gallons and the mean is 15.915.9 gallons per day. If they are using a 85%85% level of confidence, how large of a sample is required to estimate the mean usage of water? Round your answer up to the next integer.

Answer 1

We have given here,                  
                  
Population standard deviation =1.3  
Margin of error =E=0.14  
Level of significance =   1-0.85=0.15  
Z critical value is (by using Z table)=   1.44  
Sample size formula is                   

n=179