University Hospital has been concerned with the number of errors found in its billing statements to patients. An audit of 100 bills per week over the past 12 weeks revealed the following number of errors:
Week 1 Errors 4
week 2 errors 5
week 3 errors 6
week 4 errors 6
week 5 errors 3
week 6 errors 2
week 7 errors 6
week 8 errors 7
week 9 errors 3
week 10 errors 4
week 11 errors 3
week 12 errors 4
(a) develop control charts with z=3
(b) is the process in control?