An energy company changed its billing method in a small town claiming that the change would decrease the mean energy bill for customers. Under the old plan the mean monthly cost in the town was $225....

An energy company changed its billing method in a small town claiming that the change would decrease the mean energy bill for customers. Under the old plan the mean monthly cost in the town was $225.  To test the claim a sample of 47 energy bills were checked and the mean bill was $211 with a standard deviation of $89.  Show all the steps and work to test the company’s claim at the 5% significance level.