water usage is closely watched in many parts of australia. suppose that in summer the average household usage in hobart is 408litres per day. A year later it examines records of a sample of 50 households and finds that there is a daily mean usage of 380 litres with a standard deviation of 25 litres.

a. construct a 99% confidence interval for the population mean daily water usage in the second summer . Assume the population usage is normally distributed. do you think the water usage has changed in the second summer.