Textbook question. Not using for work other then to further understand the subject. Question 8.

Textbook question. Need help in understanding how this is done. Not using for work other then to further understand the subject.

Question 8.16

Suppose that Syd Water monitors water usage in a suburb and finds that for one summer the average household usage is 408 litres 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.

• Construct a 95% confidence interval for the population

mean daily water usage in the second summer. Assume the

population usage is normally distributed.

• Interpret the interval constructed in (the question above).
• Do you think water usage has changed in the second

summer? Explain.