Hello, Can anyone please explain how to find the critical value? For example z0.01= 1.28, how do you find the 1.28? 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 0.13 gallons. A previous study found that for an average family the standard deviation is 1.3 gallons and the mean is 18.5 gallons per day. If they are using a 98% 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.