Test-Bank-for-Heizer-Operations-Management-9e

44.The mean and standard deviation for a process for which we have a substantial history are x = 120 and σ = 2. For the variable control chart, a sample size of 16 will be used. What is the mean of the sampling distribution?

a.1/8 (0.125)

b.0.5

c.2

d.40

e.none of the above

e (Statistical Process Control (SPC), moderate) {AACSB: Analytic Skills}

45.Jars of pickles are sampled and weighed. Sample measures are plotted on control charts. The ideal weight should be precisely 11 oz. Which type of chart(s) would you recommend?

a.p-charts

b.c-charts

c.x - and R-charts

d.x -, but not R-charts

e.both p- and c-charts

c (Statistical Process Control (SPC), moderate)

46.If x = 23 ounces, σ = 0.4 ounces, and n = 16, the ±3σ control limits will be

a.21.8 to 24.2 ounces

b.23 ounces

c.22.70 to 23.30 ounces

d.22.25 to 23.75 ounces

e.none of the above

c (Statistical Process Control (SPC), moderate) {AACSB: Analytic Skills}

47.The usual purpose of an R-chart is to signal whether there has been a

a.gain or loss in dispersion

b.change in the percent defective in a sample

c.change in the central tendency of the process output

d.change in the number of defects in a sample

e.none of the above

a (Statistical Process Control (SPC), moderate)

48.A manager wishes to build a 3σ range chart for a process. The sample size is five, the mean of

sample means is 16.01, and the average range is 5.3. From Table S6.1, the appropriate value of D3 is 0, and D4 is 2.115. The UCL and LCL for this range chart are

a.33.9 and 11.2

b.33.9 and 0

c.11.2 and 0

d.6.3 and 0

e.31.91 and 0.11

c (Statistical Process Control (SPC), moderate) {AACSB: Analytic Skills}

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49.Plots of sample ranges indicate that the most recent value is below the lower control limit. What course of action would you recommend?

a.Since there is no obvious pattern in the measurements, variability is in control.

b.One value outside the control limits is insufficient to warrant any action.

c.Lower than expected dispersion is a desirable condition; there is no reason to investigate.

d.The process is out of control; reject the last units produced.

e.Variation is not in control; investigate what created this condition.

e (Statistical Process Control (SPC), difficult)

50.To set x -chart upper and lower control limits, one must know the process central line, which is the

a.average of the sample means

b.total number of defects in the population

c.percent defects in the population

d.size of the population

e.average range

a (Statistical Process Control (SPC), moderate)

51.According to the text, the most common choice of limits for control charts is usually

a.± 1 standard deviation

b.± 2 standard deviations

c.± 3 standard deviations

d.± 3 standard deviations for means and ± 2 standard deviations for ranges

e.none of the above

c (Statistical Process Control (SPC), moderate)

52.Which of the following is true of a p-chart?

a.The lower control limit is found by subtracting a fraction from the average number of defects.

b.The lower control limit indicates the minimum acceptable number of defects.

c.The lower control limit may be below zero.

d.The lower control limit may be at zero.

e.The lower control limit is the same as the lot tolerance percent defective.

d (Statistical Process Control (SPC), moderate)

53.The normal application of a p-chart is in

a.process sampling by variables

b.acceptance sampling by variables

c.process sampling by attributes

d.acceptance sampling by attributes

e.none of the above

c (Statistical Process Control (SPC), moderate)

54.The statistical process chart used to control the number of defects per unit of output is the

a.x -chart

b.R-chart

c.p-chart

d.AOQ chart

e c-chart

e (Statistical Process Control (SPC), moderate)

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55.The c-chart signals whether there has been a

a.gain or loss in uniformity

b.change in the number of defects per unit

c.change in the central tendency of the process output

d.change in the percent defective in a sample

e.change in the AOQ

b (Statistical Process Control (SPC), moderate)

56.The local newspaper receives several complaints per day about typographic errors. Over a sevenday period, the publisher has received calls from readers reporting the following number of errors: 4, 3, 2, 6, 7, 3, and 9. Based on these data alone, what type of control chart(s) should the publisher use?

a.p-chart

b.c-chart

c.x -chart

d.R-chart

e.x - and R-charts

b (Statistical Process Control (SPC), moderate)

57.A manufacturer uses statistical process control to control the quality of the firm's products. Samples of 50 of Product A are taken, and a defective/acceptable decision is made on each unit sampled. For Product B, the number of flaws per unit is counted. What type(s) of control charts should be used?

a.p-charts for A and B

b.p-chart for A, c-chart for B

c.c-charts for both A and B

d.p-chart for A, mean and range charts for B

e.c-chart for A, mean and range charts for B

b (Statistical Process Control (SPC), difficult)

58.A nationwide parcel delivery service keeps track of the number of late deliveries (more than 30 minutes past the time promised to clients) per day. They plan on using a control chart to plot their results. Which type of control chart(s) would you recommend?

a.x - and R-charts

b.p-charts

c.c-charts

d.x -, but not R-charts

e.both p- and c-charts

c (Statistical Process Control (SPC), moderate)

59.A run test is used

a.to examine variability in acceptance sampling plans

b.in acceptance sampling to establish control

c.to examine points in a control chart to check for natural variability

d.to examine points in a control chart to check for nonrandom variability

e.none of the above

d (Statistical Process Control (SPC), moderate)

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60.Which of the following is true regarding the process capability index Cpk?

a.A Cpk index value of 1 is ideal, meaning all units meet specifications.

b.The larger the Cpk, the more units meet specifications.

c.The Cpk index can only be used when the process centerline is also the specification centerline.

d.Positive values of the Cpk index are good; negative values are bad.

e.None of the above is true.

b (Process capability, moderate)

61.If the Cpk index exceeds 1

a.the AQL must be smaller than the LTPD

b.σ must be less than one-third of the difference between the specification and the process mean

c.the x-bar chart must indicate that the process is in control

d.the process is capable of Six Sigma quality

e.the process is characterized as "not capable"

b (Process capability, moderate)

62.The statistical definition of Six Sigma allows for 3.4 defects per million. This is achieved by a Cpk index of

a.0

b.1

c.1.33

d.1.67

e.2

e (Process capability), moderate)

63.A Cpk index of 1.00 equates to a defect rate of

a.five percent

b.3.4 defects per million

c.2.7 per 1,000 items

d.97.23 percent

e.one percent

c (Process capability, moderate)

64.Acceptance sampling

a.is the application of statistical techniques to the control of processes

b.was developed by Walter Shewhart of Bell Laboratories

c.is used to determine whether to accept or reject a lot of material based on the evaluation of a sample

d.separates the natural and assignable causes of variation

e.all of the above

c (Acceptance sampling, moderate)

65.Acceptance sampling's primary purpose is to

a.estimate process quality

b.estimate lot quality

c.detect and eliminate defectives

d.decide if a lot meets predetermined standards

e.determine whether defective items found in sampling should be replaced

d(Acceptance sampling, difficult)

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66.An acceptance sampling plan's ability to discriminate between low quality lots and high quality lots is described by

a.a Gantt chart

b.the Central Limit Theorem

c.a process control chart

d.an operating characteristics curve

e.a range chart

d (Acceptance sampling, moderate)

67.Acceptance sampling

a.may involve inspectors taking random samples (or batches) of finished products and measuring them against predetermined standards

b.may involve inspectors taking random samples (or batches) of incoming raw materials and measuring them against predetermined standards

c.is more economical than 100% inspection

d.may be either of a variable or attribute type, although attribute inspection is more common in the business environment

e.All of the above are true.

e (Acceptance sampling, moderate)

68.Which of the following statements on acceptance sampling is true?

a.Acceptance sampling draws samples from a population of items, tests the sample, and accepts the entire population if the sample is good enough, and rejects it if the sample is poor enough.

b.The sampling plan contains information about the sample size to be drawn and the critical acceptance or rejection numbers for that sample size.

c.The steeper an operating characteristic curve, the better its ability to discriminate between good and bad lots.

d.All of the above are true.

e.All of the above are false.

d (Acceptance sampling, moderate)

69.Acceptance sampling is usually used to control

a.the number of units output from one stage of a process which are then sent to the next stage

b.the number of units delivered to the customer

c.the quality of work-in-process inventory

d.incoming lots of purchased products

e.all of the above

d (Acceptance sampling, moderate)

70.An operating characteristic (OC) curve describes

a.how many defects per unit are permitted before rejection occurs

b.the sample size necessary to distinguish between good and bad lots

c.the most appropriate sampling plan for a given incoming product quality level

d.how well an acceptance sampling plan discriminates between good and bad lots

e.none of the above

d (Acceptance sampling, moderate)

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71.An operating characteristics curve shows

a.upper and lower product specifications

b.product quality under different manufacturing conditions

c.how the probability of accepting a lot varies with the population percent defective

d.when product specifications don't match process control limits

e.how operations affect certain characteristics of a product

c (Acceptance sampling, moderate)

72.Producer's risk is the probability of

a.accepting a good lot

b.rejecting a good lot

c.rejecting a bad lot

d.accepting a bad lot

e.none of the above

b (Acceptance sampling, moderate)

73.Which of the following is true regarding the relationship between AOQ and the true population percent defective?

a.AOQ is greater than the true percent defective.

b.AOQ is the same as the true percent defective.

c.AOQ is less than the true percent defective.

d.There is no relationship between AOQ and the true percent defective.

e.The relationship between these two cannot be determined.

c (Acceptance sampling, difficult)

74.Average outgoing quality (AOQ) usually

a.worsens with inspection

b.stays the same with inspection

c.improves with inspection

d.may either improve or worsen with inspection

e.is the average quality before inspection

c (Acceptance sampling, moderate)

75.A Type I error occurs when

a.a good lot is rejected

b.a bad lot is accepted

c.the number of defectives is very large

d.the population is worse than the AQL

e.none of the above

a (Acceptance sampling, moderate)

76.A Type II error occurs when

a.a good lot is rejected

b.a bad lot is accepted

c.the population is worse than the LTPD

d.the proportion of defectives is very small

e.none of the above

b (Acceptance sampling, moderate)

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77.In most acceptance sampling plans, when a lot is rejected, the entire lot is inspected and all defective items are replaced. When using this technique the AOQ

a.worsens (AOQ becomes a larger fraction)

b.improves (AOQ becomes a smaller fraction)

c.is not affected, but the AQL is improved

d.is not affected

e.falls to zero

b (Acceptance sampling, moderate)

78.An acceptance sampling plan is to be designed to meet the organization's targets for product quality and risk levels. Which of the following is true?

a.n and c determine the AQL.

b.AQL, LTPD, α and β collectively determine n and c.

c.n and c are determined from the values of AQL and LTPD.

d.α and β are determined from the values of AQL and LTPD.

e.None of the above is true.

b (Acceptance sampling, moderate)

79.A lot that is accepted by acceptance sampling

a.has more defects than existed before the sampling

b.has had all its defects removed by 100% inspection

c.will have the same defect percentage as the LTPD

d.has no defects present

e.All of the above are false.

e (Acceptance sampling, moderate)

80.Which of the following statements about acceptance sampling is true?

a.The steeper an OC curve, the better it discriminates between good and bad lots.

b.Acceptance sampling removes all defective items.

c.Acceptance sampling of incoming lots is replacing statistical process control at the supplier.

d.Acceptance sampling occurs continuously along the assembly line.

e.All of the above are true.

a (Acceptance sampling, moderate)

81.Which of the following is true regarding the average outgoing quality level?

a.An AOQ value of 1 is ideal, because all defects have been removed.

b.AOQ is always greater than AQL but less than LTPD.

c.AOQ rises (worsens) following inspection of failed lots.

d.AOQ is very low (very good) for extremely poor quality lots.

e.None of the above is true.

d (Acceptance sampling, difficult)

FILL-IN-THE-BLANK

82._____________ is variation in a production process that can be traced to specific causes.

Assignable variation (Statistical Process Control (SPC), moderate)

83.The _________ is the chief way to control attributes.

P-chart (Statistical Process Control (SPC), moderate)

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84.If a process has only natural variations, _________ percent of the time the sample averages will fall inside the ±3σn (or ±3σx ) control limits.

99.73 (Statistical Process Control (SPC), easy)

85.The _________ is a quality control chart that indicates when changes occur in the central tendency of a production process.

x-bar chart (Statistical Process Control (SPC), moderate)

86.The _________ are calculated to show how much allowance should be made for natural variation.

UCL and LCL, or upper and lower control limits (Statistical Process Control (SPC), easy)

87.The _________ is a quality control chart used to control the number of defects per unit of output. c-chart (Statistical Process Control (SPC), moderate)

88.The term _________ is used to describe how well a process makes units within design specifications (or tolerances).

process capability (Process capability, moderate)

89.A Cpk index greater than _________ is a capable process, one that generates fewer than 2.7 defects

per 1000 at the ± 3σ level.

unity, or 1 (Process capability, moderate)

90.___________ is a method of measuring samples of lots or batches of product against predetermined standards.

Acceptance sampling (Acceptance sampling, moderate)

91.A(n) _____________ is a graph that describes how well an acceptance plan discriminates between good and bad lots.

OC or operating characteristics curve (Acceptance sampling, moderate)

92.The __________ is the poorest level of quality that we are willing to accept.

AQL or acceptable quality level (Acceptance sampling, moderate)

93.The ____________ is the percent defective in an average lot of goods inspected through acceptance sampling.

AOQ or average outgoing quality (Acceptance sampling, moderate)

SHORT ANSWER

94.What is the basic objective of a process control system?

It is to provide a statistical signal when assignable causes of variation are present. (Statistical Process Control (SPC), moderate)

95.Briefly explain what the Central Limit Theorem has to do with control charts.

The CLT underlies the distribution of sample means and the standard deviation of sample means. It leads to the usability of the normal distribution in control charts. (Statistical Process Control (SPC), moderate)

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96.What are the three possible results (or findings) from the use of control charts?

The results of a control chart can indicate (a) in control and capable, (b) in control but not capable, and (c) out of control. (Statistical Process Control (SPC), moderate)

97.Why do range charts exist? Aren't x-bar charts enough?

Range charts and mean charts perform different functions. The mean chart is used to detect changes in the average of a process. But that average might stay the same while output is getting more scattered. The purpose of the range chart is to detect changes in the dispersion of a process. (Statistical Process Control (SPC), moderate)

98.Examine the Statistical Process Control outputs below. Answer the following questions.

a.What is the sample size?

b.What is the number of samples?

c.What is the mean of sample 8; what is the range of sample 10?

d.. Is this process in control? Explain--a simple Yes or No is insufficient. e. What additional steps should the quality assurance team take?

		Mean			Range
UCL (Upper control limit)		12.6856			1.0193
CL (Center line)		12.36			0.67
LCL (Lower control limit)		12.0344			0
Sample Number	Item1	Item2		Item3			Item4	Mean	Range
Sample 1	12.2	12.6		12		12.1		12.225	0.6
Sample 2	11.9	12.5		12.4		12.7		12.375	0.8
Sample 3	12	12.2		12.9		13.1		12.55	1.1
Sample 4	12.5	12.5		12.4		12.8		12.55	0.4
Sample 5	12.2	12.8		12.7		12		12.425	0.8
Sample 6	12.1	12.5		11.8		12.3		12.175	0.7
Sample 7	12.3	12.4		12.8		12.4		12.475	0.5
Sample 8	12	12.1		12.4		12.2		12.175	0.4
Sample 9	12.1	12.8		12.4		11.9		12.3	0.9
Sample 10	12.6	12.4		12.1			12.3	12.35	0.5

The sample size is 4; ten samples were taken. The mean of sample 8 is 12.175; the range of sample 10 is 0.5. This chart is built on 2-sigma limits, so the probability of a false signal is about 4.5%. The process is not in control—while all means are within limits, the range for sample 3 is too large. Investigate for assignable cause and eliminate that cause.

(Statistical Process Control (SPC), difficult) {AACSB: Analytic Skills}

99.Can "in control" and "capable" be shown on the same chart?

Only indirectly. The chart illustrating control plots the averages of small samples, while "Capability" is based on the dimensions of individual units. Figure S6.2 suggests that an overly wide range for sample means implies an overly large range for individual values as well. (Statistical Process Control (SPC), moderate)

100.What is the difference between natural and assignable causes of variation?

Natural variations are those variations that are inherent in the process and for which there is no identifiable cause. These variations fall in a natural pattern. Assignable causes are variations beyond those that can be expected to occur because of natural variation. These variations can be traced to a specific cause. (Statistical Process Control (SPC), moderate)

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101.Why are X and R-charts usually used hand in hand?

The ultimate goal of the X and R-charts is to ascertain, by a sampling procedure, that the relevant parameter is kept within specific upper and lower bounds. The X-bar chart alone tells us only that the average or variable values are within the appropriate limits. The combination of X and the R-charts allows one to determine that both the average and the deviations are within the limits. (Statistical Process Control (SPC), moderate)

102.What does it mean for a process to be "capable"?

Process capability implies that the natural variation of the process must be small enough to produce products that meet the specifications or tolerances required. (Process capability, moderate)

103.What is the difference between the process capability ratio Cp and the process capability index Cpk?

The Cp ratio does not consider how well the process average is centered on the target value. However, Cpk does consider how well the process is centered. (Process capability, moderate)

104.A process is operating in such a manner that the mean of the process is exactly on the lower specification limit. What must be true about the two measures of capability for this process?

The Cp ratio does not consider how well the process average is centered on the target value; its value is unaffected by the setting for the process mean. However, Cpk does consider how well the process is centered; with x-bar on the LSL, the formula guarantees a Cpk of zero.

(Process capability, moderate)

105.What is acceptance sampling?

Acceptance sampling is a method of measuring random samples of lots or batches of products against predetermined standards. (Acceptance sampling, moderate)

106.Why doesn't acceptance sampling remove all defects from a batch?

Acceptance sampling is a method of measuring random samples of lots or batches of products against predetermined standards. Acceptance sampling is not 100 percent inspection. Based on sampling results, the entire batch is either accepted or rejected. A batch may contain small numbers of defects and still meet the standard for acceptance. (Acceptance sampling, moderate)

107.What is the purpose of the Operating Characteristics curve?

An OC curve plots the probability of acceptance against the percentage of defects in the lot. It therefore shows how well an acceptance sampling plan discriminates between good and bad lots. (Acceptance sampling, moderate)

108.What is the AOQ of an acceptance sampling plan?

The AOQ is the average outgoing quality. It is the percent defective in an average lot of goods inspected through an acceptance sampling plan. (Acceptance sampling, moderate)

109.Define consumer's risk. How does it relate to the errors of hypothesis testing? What is the symbol for its value?

The consumer's risk is the probability of accepting a bad lot. It is a Type II error; its value is beta. (Acceptance sampling, moderate)

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