An ad agency tracks the complaints, by week received, about the billboards in its city:

Week No. of Complaints

1........... 4

2........... 5

3........... 4

4...........11

5........... 3

6........... 9

(a) What type of control chart would you use to monitor this process and why?

(b) What are the 3-sigma control limits for this process? Assume that the historical complaint rate is unknown.

(c) Is the process mean in control, according to the control limits?

(d) Assume now that the historical complaint rate has been four calls a week. What would the 3-sigma control limits for this process be now? Is the process in control according to the control limits?