Question: Boston-based Legal Seafoods prides itself on having instituted an advanced quality control system that includes the control of both food quality and service quality. The following are successive service times at one of the chain's restaurants on a Saturday night in May 2007 (time is stated in minutes from customer entry to appearance of waitperson):
5, 6, 5, 5, 5, 7, 4, 12, 4.5, 2.5, 5.5, 6, 6, 13, 2, 5, 4, 4.5, 6.5, 4, 1, 2, 3, 5.5, 4, 4, 8, 12, 3, 4.5, 6.5, 6, 7, 10, 6, 6.5, 5, 3, 6.5, 7
Aggregate the data into groups of four, and construct a control chart for the process mean. Is the waiting time at the restaurant under control?