A supervisor has noticed that sales for all departments world wide has been averaging $12,000 a month for a number of years. For the last 18 review periods the average sales figure has dropped to $11,500 with a standard deviation of $4,000. Management is concerned. Perform a hypothesis test to determine if this change in sales is a potential problem.
a) Use a 1 % alpha for this analysis
b) Make a recommendation to management based on your result