Operations Management Supplement 6: Statistical Process Control

Question 15. A manufacturing engineer is designing a process that must be able to produce a shaft with a diameter of 2.5 cm plus or minus 0.01 cm. If the process capability must be 1.5, what is the maximum process standard deviation? A. 0.00222 B. 0.0133 C. 2.49 - 2.51 D. 0.02

A. 0.00222

Question 13. For the last 30 days, the number of mistakes on the daily report has averaged 4.5. What would the UCL be if a 3-sigma c-chart was constructed? A. 10.86 B. 2.12 C. 18 D. 7.5

A. 10.86

Question 3. C-charts are based on the A. Poisson distribution. B. binomial distribution. C. normal distribution. D. Erlang distribution.

A. Poisson distribution.

Question 8. In acceptance sampling, the producer's risk is the risk of having a A. good lot rejected. B. bad lot accepted. C. good lot accepted. D. bad lot rejected.

A. good lot rejected.

Question 7. The R-chart A. is used to indicate gains or losses in uniformity. B. generally uses control limits set at plus or minus 2 standard deviations of the distribution, rather than plus or minus 3 which is commonly used on the X-bar chart. C. is used to measure changes in the central tendency. D. is always in control if the X-bar chart is in control.

A. is used to indicate gains or losses in uniformity.

Question 2. One type of control chart for attributes is a A. p-chart. B. R-chart. C. CPK chart. D. x-bar chart.

A. p-chart. .

Question 12. A customer service hotline has received an average of 7 complaints a day for the last 25 days. What type of control chart should be used to monitor this hotline? A. R-chart B. c-chart C. p-chart D. X-bar chart

B. c-chart

Question 5. Process capability A. exists when the process is perfectly centered. B. means that the natural variation of the process must be small enough to produce products that meet the standard. C. exists when CPK is less than 1.0. D. cannot be measured.

B. means that the natural variation of the process must be small enough to produce products that meet the standard.

Question 11. Twenty samples of size 100 are taken. The total number of defective items is 75. What is the UCL of the 3-sigma (z=3) p-chart? A. .0375 B. 0.793 C. .094 D. .165

C. .094

Question 17. A box of 1000 parts is subjected to an acceptance sampling plan that examines only 50 parts. The actual fraction defective in the box is 0.02 and the sampling plan has a 0.53 probability of accepting a box of this quality. What is the average outgoing quality for this scenario? A. 0.53 B. 0.02 C. 0.01 D. 0.51

C. 0.01

Question 14. A bottling company runs a filling process that should fill bottles with 12 plus or minus 0.04 ounces. A capability study reveals that the process mean is 12 ounces and the standard deviation is 0.01 ounces. What is the capability of the bottling process? A. 1.5 B. 0.75 C. 1.33 D. 0.67

C. 1.33

Question 10. Twenty samples of size 5 are taken from a stable process. The average means of the sample means is 42.5, and the average range of the samples is 1.5. What is the UCL for the R-chart? **NOTE** Table S6.1, Factors for Computing Control Chart Limits, is available in the Hint portion of this question. A. 0.00 B. 1.5 C. 3.17 D. 43.37

C. 3.17

Question 9. Twenty samples of size 5 are taken from a stable process. The average means of the sample means is 42.5, and the average range of the samples is 1.5. What is the UCL for the X-bar chart? **NOTE** Table S6.1, Factors for Computing Control Chart Limits, is available in the Hint portion of this question. A. 42.5 B. 3.17 C. 43.37 D. 47.0

C. 43.37

Question 16. Which is the best statement regarding an operating characteristic curve? A. As the fraction defective increases, the probability of accepting the lot also increases. B. As the fraction defective decreases, the probability of accepting the lot also decreases. C. As the AQL decreases, the producer's risk also decreases. D. As the lot tolerance percent defective decreases, the consumer's risk also decreases.

C. As the AQL decreases, the producer's risk also decreases.

Question 1. Which type of control chart should be used when it is possible to have more than one mistake per item? A. p-chart B. x-bar chart C. R-chart D. c-chart

D. c-chart

Question 6. The object of a statistical process control (SPC) system is to A. eliminate natural variation. B. assess the customer expectations. C. provide a signal when natural variations are present. D. provide a signal when assignable variations are present.

D. provide a signal when assignable variations are present.

Question 4. If a sample of parts is measured and the mean of the sample measurements is outside the control limits A. the process is in control, but not capable of producing within the established control limits. B. The process variance must also be in control. C. the process is within the established control limits with only natural causes of variation. D. the process is out of control and the cause can be established.

D. the process is out of control and the cause can be established.

8. When the process fraction defective is low, the p-chart may have a negative lower control limit. True False

False

9. Six sigma capability means that the process specifications are six standard deviations wide. True False

False

Question 12. If a process is in control, then all of the output produced is acceptable for use. True False

False

Question 2. When the process average is under control, the process dispersion is also under control. True False

False

Question 4. Control charts for variables classify items as defective or not defective. True False

False

Question 7. For a process exhibiting only natural variation, 95% of the sample averages will fall within three standard deviations of the sampling distribution. True False

False

Question 1. A process is said to be operating in statistical control when the only natural variation is present. True False

True

Question 10. If the producer's risk increases, then the consumer's risk decreases. True False

True

Question 11. The average outgoing quality limit (AOQL) tells the producer the maximum fraction defective possible for a sampling plan. True False

True

Question 3. The central limit theorem states that regardless of the distribution of all parts (or services), the distribution of x-bars will tend to follow a normal curve as the number of samples increases. True False

True

Question 5. One popular measure of process capability is Cpk. True False

True

Question 6. Acceptance sampling is a form of testing that involves taking random samples of lots or batches of products and comparing them against predetermined standards. True False

True