A textile manufacturer wants to set up a control chart for irregularities (e.g., oil stains, shop soil, loose threads, and tears) per 100 square yards of carpet. The following data were collected from a sample of twenty 100 square yard pieces of carpet.
Sample Irregularities Sample Irregularities Sample Irregularities Sample Irregularities
1 14 6 15 11 6 16 14
2 9 7 11 12 15 17 7
3 5 8 14 13 14 18 15
4 17 9 17 14 19 19 11
5 9 10 15 15 13 20 6
a. Using these data, set up a c-chart with z=3.
The UCL
equals _____ and the LCL
equals _____.
b. Suppose that the next five samples had 19, 19, 10, 11, and 19 irregularities. What do you conclude?
A. At least one of the sample points is within the control limits, so the process is in control.
B. At least one of the sample points is outside the control limits, so the process is not in control.
C. All of the sample points are within the control limits, so the process is in control.
D. All of the sample points are within the control limits, so the process is not in control.
E. At least one sample point is less than the upper control limit, so the process is not in control.
F. At least one of the sample points is greater than the lower control limit, so the process is not in control.