1. ABC company is producing printed circuit boards (PCBs) used in laptop computers. The associated manufacturing process which is in 3s-control seems to fluctuate in quality recently. The following table presents the number of nonconformities observed in 26 successive samples of 100 PCBs over time. One nonconformity represents one defect on a PCB. But one PCB may have more than one nonconformity.

Sample number	Number of conformities	Sample Number	Number of conformities
1	21	14	19
2	24	15	10
3	16	16	30
4	12	17	28
5	15	18	35
6	39	19	18
7	28	20	39
8	20	21	30
9	36	22	37
10	25	23	16
11	20	24	19
12	24	25	17
13	16	26	15

Questions

a. What control chart should ABC use to monitor the PCB manufacturing process if the company wants to monitor the number of nonconformity over time. (4 marks)

b. What are the upper and lower control limits? (MUST show the control chart you choose and demonstrate the calculations of the limits) (4 marks)

c. Which sample(s) shows the process is out of control? (4 marks)

d. What are the new control limits after removing the samples identified in #c ? (MUST show the new control chart)