Operations Management - Chapter 10

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_______ variation is a variation whose cause can be identified. A. ASSIGNABLE B. Controllable C. Random D. Statistical E. Theoretical

A. Assignable

A control chart used to monitor the fraction of defectives generated by a process is the: A. p-chart B. R-chart C. x-bar chart D. c-chart E. Gantt chart

A. p-chart

Studies on a machine that molds plastic water pipe indicate that when it is injecting 1-inch diameter pipe, the process standard deviation is 0.05 inches. The one-inch pipe has a specification of 1-inch plus or minus 0.10 inch. What is the process capability index (Cpk) if the long-run process mean is 1 inch? A. 0.50 B. 0.67 C. 1.00 D. 2.00 E. none of the above

B. 0.67

The specifications for a product are 6 mm ± 0.1 mm. The process is known to operate at a mean of 6.05 with a standard deviation of 0.01 mm. What is the Cpk for this process? A. 3.33 B. 1.67 C. 5.00 D. 2.50 E. none of the above

B. 1.67

A process results in a few defects occurring in each unit of output. Long-run, these defects should be monitored with ___________. A. p-charts B. C-CHARTS C. x-bar charts D. r-charts E. o-charts

B. c-charts

The more effective and all-encompassing a firm's quality control and continuous improvement efforts, the less that company will need to rely on: A. insourcing. B. inspection. C. outsourcing. D. acceptance sampling. E. capability assessment.

B. inspection.

The basis for a statistical process control chart is a (the) __________. A. process capability B. SAMPLING DISTRIBUTION C. control limit D. sample range E. sample mean

B. sampling distribution

A shift in the process mean for a measured characteristic would most likely be detected by a: A. p-chart B. X-BAR CHART C. c-chart D. R-chart E. s-chart

B. x-bar chart

The specification limit for a product is 8 cm and 10 cm. A process that produces the product has a mean of 9.5 cm and a standard deviation of 0.2 cm. What is the process capability, Cpk? A. 3.33 B. 1.67 C. 0.83 D. 2.50 E. none of the above

C. 0.83

A time-ordered plot of sample statistics is called a(n) ______ chart. A. Statistical B. Inspection C. CONTROL D. SIMO E. Limit

C. Control

A time-ordered plot of representative sample statistics is called a: A. Gantt chart B. SIMO-chart C. Control Chart D. Up-Down Matrix E. Standard deviation table

C. Control Chart

If a process is performing as it should, it is still possible to obtain observations which are outside of which limits? (I) tolerances (II) control limits (III) process variability A. I B. II C. I and II D. II and III E. I, II, and III

C. I and II

A plot below the lower control limit on the range chart: (I) should be ignored since lower variation is desirable (II) may be an indication that process variation has decreased (III) should be investigated for assignable cause A. I and II B. I and III C. II and III D. II only E. I, II, and III

C. II and III

Which of the following relationships must always be incorrect? A. Tolerances > process variability > control limits B. Process variability > tolerances > control limits C. Tolerances > control limits > process variability D. Process variability > control limits > tolerances E. Process variability <Tolerances<control limits

C. Tolerances > control limits > process variability

Which of the following is not a step in the quality control process? A. define what is to be controlled B. compare measurements to a standard C. eliminate each of the defects as they are identified D. take corrective action if necessary E. evaluate corrective action

C. eliminate each of the defects as they are identified

The optimum level of inspection occurs when we catch at least 98.6 percent of the defects.

FALSE

The primary purpose of statistical process control is to detect a defective product before it is shipped to a customer.

FALSE

The process capability index (indicated by Cpk) can be used only when the process is centered.

FALSE

The purpose of statistical process control is to ensure that historical output is random.

FALSE

Tolerances represent the control limits we use on the charts.

FALSE

Type I and Type II errors refer to the magnitude of variation from the standard.

FALSE

The greater the capability ratio, the higher the rejects.

FALSE

The larger the process variation, the tighter the specifications should be.

FALSE

The number of defective parts in a sample is an example of variable data because it will "vary" from one sample to another.

FALSE

A point which is outside of the lower control limit on an R-chart: A. is an indication that no cause of variation is present B. should be ignored because it signifies better than average quality C. should be investigated because an assignable cause of variation might be present D. should be ignored unless another point is outside that limit E. is impossible since the lower limit is always zero

C. should be investigated because an assignable cause of variation might be present

A p-chart would be used to monitor _______. A. average shrinkage B. dispersion in sample data C. the fraction defective D. the number of defects per unit E. the range of values

C. the fraction defective

A control chart used to monitor the process mean is the: A. p-chart B. R-chart C. x-bar chart D. c-chart E. Gantt chart

C. x-bar chart

When a process is in control, it results in there being, on average, 16 defects per unit of output. C-chart limits of 4 and 28 would lead to a _______ chance of a Type I error. A. 67% B. 92% C. 33% D. 0.3% E. 5%

D. 0.3%

Studies on a bottle-filling machine indicates it fills bottles to a mean of 16 ounces with a standard deviation of 0.10 ounces. What is the process specification, assuming the Cpk index of 1? A. 0.10 ounces B. 0.20 ounces C. 0.30 ounces D. 16.0 ounces plus or minus 0.30 ounces E. none of the above

D. 16.0 ounces plus or minus 0.30 ounces

The probability of concluding that assignable variation exists when only random variation is present is: (I) the probability of a Type I error (II) known as the alpha risk (III) highly unlikely (IV) the sum of probabilities in the two tails of the normal distribution A. I and II B. I and IV C. II and III D. I, II, and IV E. I, III, and IV

D. I, II, and IV

A control chart used to monitor the number of defects per unit is the: A. p-chart B. R-chart C. x-bar chart D. c-chart E. Gantt chart

D. c-chart

The purpose of control charts is to: A. estimate the proportion of output that is acceptable B. weed out defective items C. determine if the output is within tolerances/specifications D. distinguish between random variation and assignable variation in the process E. provide meaningful work for quality inspectors

D. distinguish between random variation and assignable variation in the process.

The optimum level of inspection is where the: A. cost of inspection is minimum B. cost of passing defectives is minimum C. total cost of inspection and defectives is maximum D. total cost of inspection and defectives is MINIMUM E. difference between inspection and defectives costs is minimum

D. total cost of inspection and defectives is minimum

Organizations should work to improve process capability so that quality control efforts can become more ________. A. effective B. efficient C. necessary D. UNNECESSARY E. widespread

D. unnecessary

The range chart (R-chart) is most likely to detect a change in: A. proportion B. mean C. number defective D. VARIABILITY E. sample size

D. variability

When a process is in control, it results in there being, on average, 16 defects per unit of output. C-chart limits of 8 and 24 would lead to a _______ chance of a Type I error. A. 67% B. 92% C. 33% D. .03% E. 5%

E. 5%

The process capability index (Cpk) may mislead if: (I) the process is not stable. (II) the process output is not normally distributed. (III) the process is not centered. A. I and II B. I and III C. II and III D. II only E. I, II and III

E. I, II and III

Inspection is a(n): A. prevention. B. control. C. monitoring. D. corrective. E. appraisal.

E. appraisal.

Quality control, in contrast to quality assurance, is implemented: A. after production. B. before inspection. C. by self-directed teams. D. by top management. E. during production.

E. during production.

A c-chart is used for: A. means B. ranges C. percent defective D. fraction defective per unit E. number of defects per unit

E. number of defects per unit

Which of the following quality control sample statistics indicates a quality characteristic that is an attribute? A. mean B. variance C. standard deviation D. range E. proportion

E. proportion

A c-chart is used to monitor the total number of defectives in the output of a process.

FALSE

A process that exhibits random variability would be judged to be out of control.

FALSE

An "up and down" run test uses the median as a reference point and measures the percentage above and below the median.

FALSE

An R value of zero (on a range chart) means that the process must be in control since all sample values are equal.

FALSE

An x-bar control chart can only be valid if the underlying population it measures is a normal distribution.

FALSE

Approving the effort that occurs during the production process is known as acceptance sampling.

FALSE

Approximately 99.7% of sample means will fall within ± two standard deviations of the process mean if the process is under control.

FALSE

Attributes need to be measured, variable data can be counted.

FALSE

Control limits are based on multiples of the process standard deviation.

FALSE

Control limits used on process control charts are specifications established by design or customers.

FALSE

Even if the process is not centered, the process capability index (indicated by Cpk) is very useful.

FALSE

Larger samples will require wider x-bar control limits because there is more data.

FALSE

Low-cost, high-volume items often require more intensive inspection.

FALSE

Non-random variation is likely whenever all observations are between the LCL and UCL.

FALSE

Processes that are in control eliminate variations.

FALSE

Range charts and p-charts are both used for variable data.

FALSE

Range charts are used mainly with attribute data.

FALSE

Range control charts are used to monitor process central tendency.

FALSE

Run tests give managers an alternative to control charts; they are quicker and cost less.

FALSE

Statistical Process Control is the measurement of rejects in the final product.

FALSE

Statistical process control focuses on the acceptability of process output.

FALSE

The Taguchi Cost Function suggests that the capability ratio can be improved by extending the spread between LCL and UCL.

FALSE

The best way to assure quality is to use extensive inspection and control charts.

FALSE

"Assignable variation" is variation due to a specific cause, such as tool wear.

TRUE

"Process capability" compares "process variability" to the "tolerances."

TRUE

"Quality of conformance" is concerned with whether a product or service conforms to its specifications.

TRUE

A c-chart is used to monitor the number of defects per unit for process output.

TRUE

A lower control limit must by definition be a value less than an upper control limit.

TRUE

A p-chart is used to monitor the fraction of defectives in the output of a process.

TRUE

A run test checks a sequence of observations for randomness.

TRUE

Attribute data are counted, variable data are measured.

TRUE

Concluding a process is out of control when it is not is known as a Type I error.

TRUE

Control limits tend to be wider for more variable processes.

TRUE

High-cost, low-volume items often require careful inspection since we make them so infrequently.

TRUE

If a point on a control chart falls outside one of the control limits, this suggests that the process output is non-random and should be investigated.

TRUE

Patterns of data on a control chart suggest that the process may have non-random variation.

TRUE

Quality control is assuring that processes are performing in an acceptable manner.

TRUE

Run tests are useful in helping to identify nonrandom variations in a process.

TRUE

The amount of inspection needed is governed by the costs of inspection and the expected costs of passing defective items.

TRUE

The amount of inspection we choose can range from no inspection at all to inspecting each item numerous times.

TRUE

The optimum level of inspection minimizes the sum of inspection costs and the cost of passing defectives.

TRUE

The output of a process may not conform to specifications even though the process may be statistically "in control."

TRUE

The sampling distribution can be assumed to be approximately normal even when the underlying process distribution is not normally distributed.

TRUE

The variation of a sampling distribution is tighter than the variation of the underlying process distribution.

TRUE

Variation in a sample statistic collected from a process may be either random variation or assignable variation - or both.

TRUE

When a process is not centered, its capability is measured in a slightly different way. The symbol for this case is Cpk.

TRUE


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