Problem 1 (30 points)

A maintenance group improves the effectiveness of its repair work by monitoring the number of maintenance requests that require a second call to complete the repair. Eight weeks of data is shown in the table below.

Sample

Number

Sample

Size

Number

Nonconforming

1

100

10

2

100

15

3

100

31

4

100

18

5

100

24

6

100

12

7

100

23

8

100

15

a)Find trial control limits (UCL, CL, LCL) by hand for number nonconforming for this process.

b)Construct the trial control chart for this process using Minitab from part (a). Is the process in-control (yes or no)? Why? What should be done?

c)Assume an assignable cause was identified, Construct the revised control chart using Minitab.

d)What are the revised control limits? (no need to show calculations)