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 0.12 gallons. A previous study found that for an average family the variance is 5.29 gallons and the mean is 17 gallons per day. If they are using a 85% level of confidence, how large of a sample is required to estimate the mean usage of water

So the answer for this case would be n=762 rounded up to the nearest integer

Step-by-step explanation:

Information given

represent the mean

population mean (variable of interest)

represent the standard deviation

Solution to the problem

The margin of error is given by this formula:

   (a)

And on this case we have that ME =0.12 and we are interested in order to find the value of n, if we solve n from equation (a) we got:

  (b)

The confidence level is 85%, the significance level would be and the critical value for this case would be , replacing into formula (b) we got:

So the answer for this case would be n=762 rounded up to the nearest integer

Step-by-step explanation:

interest=90

principal=600

rate=5%

time = I × 100/p×r

= 90×100/600×5

= 3 years.