Garcia s Garage desires to create some colorful charts and graphs to illustrate

Garcia's Garage desires to create some colorful charts and graphs to illustrate how reliably its mechanics "get under the hood and fix the problem." The historic average for the proportion of customers that return for the same repair within the 30-day warranty period is 0.11. Each month, Garcia tracks 90 customers to see whether they return for warranty repairs. The results are plotted as a proportion to report progress toward the goal. If the control limits are to be set at three standard deviations on either side of the goal, determine the control limits for this chart. In March, 18 of the 90 customers in the sample group returned for warranty repairs. Is the repair process in control?