Question: 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 twelve weeks revealed the following number of errors:

Week Number of Errors

1 4

2 5

3 6

4 6

5 3

6 2

7 6

8 7

9 3

10 4

11 3

12 4

(a) Develop control charts with z = 3.

(b) Is the process in control?