1) Explain the concept of "rational subgroups". Why is it imperative that this concept is carried out in practice?
2) When would it be preferable to use an and R chart instead of anand s chart? Explain your answer.
3) When using an and R chart, what information is the chart giving you versus the R chart. Why are both needed to determine is a special cause is in the system?
4) In collecting data on average part length () from 30 subgroups, each of size 4, the following was found:
= 2400
= 45
The specifications on part length are: 81 ± 1.10:
What is the upper control limit on the R-chart?
What are the control limits on the chart?
What proportion of the parts will be nonconforming?
5) Explain the fundamental difference between a process being in control and a process being capable.
6) Explain what a Type I error would be in interpreting control charts. Explain what a Type II error would be in using control charts. How can you reduce both of these errors simultaneously?
7) Explain the fundamental differences between variables and attribute charts.
8) In the construction of control charts, why would you delete certain points?
9) Which type of control chart (p, np, c, or u) is most appropriate to monitor the following situations?
a) The manager of a plant wants to monitor the number of defective harnesses that are made daily. The plant usually makes any where from 250 to 350 harnesses a day.
b) The number of potholes in highways tracked for randomly selected one-mile segments.
c) The number of thefts in a city, over a period of time that may vary.
d) The number of seeds of a specific variety of pine tree that germinate in a nursery, when the number of seeds planted may vary.
10. The number of imperfections in paper produced by a paper mill is observed over a period of several days. During production, the operators will tear off large sections of paper and place it over a light table, and then count the imperfections. The attached excel spreadsheet shows the area inspected and the number of imperfections for 25 samples. Use Minitab to construct a control chart for the number of imperfections per square meter. Revise the limits if necessary, assuming special causes for the out-of-control points are discovered and corrected.