# Quiz 3: Statistical Process Control

Statistics

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Q 3Q 3

With acceptance sampling, a lot is either rejected or accepted depending on the number of defects found in a sample.

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Q 4Q 4

Six Sigma companies report defective parts per million (PPM) versus the more traditional defective parts per hundred.

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Q 6Q 6

Acceptance sampling involves the inspection of a non-random sample of units selected from a lot.

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Q 7Q 7

Acceptance sampling is based on the premise that a lot contains some acceptable number of defective items.

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Q 8Q 8

With a single-sample attribute plan, only one of the items randomly sampled from a lot is inspected.

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Q 9Q 9

A lot is rejected if the number of defective units found in a random sample exceeds a predetermined acceptable number of defective units.

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Q 10Q 10

An operating characteristics (OC) curve is a graph that measures the probability of accepting a lot with no defective items.

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Q 11Q 11

The consumer's risk is the probability of rejecting a lot that meets the acceptable quality level (AQL).

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Q 12Q 12

The consumer's risk is the probability of accepting a lot in which the fraction of defective items exceeds the lot tolerance percent defective (LTPD).

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Q 13Q 13

The average outgoing quality (AOQ) is a measure of the expected number of defective items that will pass on to the customer with the sampling plan selected.

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Q 16Q 16

Choosing among a single-, double- and multiple-sampling plans is a strategic versus an economic decision.

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Q 17Q 17

The probability of rejecting a lot that has an acceptable quality level is referred to as the
A) producer's risk.
B) consumer's risk.
C) lot tolerance percent defective.
D) acceptable quality level.

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Q 18Q 18

The probability of accepting a lot that has a higher percentage of defective items than the lot tolerance percent defective is referred to as the
A) producer's risk.
B) sampling plan.
C) consumer's risk.
D) average outgoing quality.

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Q 19Q 19

Six Sigma companies report
A) defective parts per million.
B) defective parts per thousand.
C) defective parts per hundred.
D) no defective parts.

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Q 20Q 20

Acceptance sampling is still used today for all the following reasons except
A) government regulations.
B) contractual requirements.
C) industry standards.
D) total quality management principles.

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Q 21Q 21

The acceptable quality level is
A) the maximum number of defective items a consumer will accept in a lot.
B) an acceptable proportion of defective items in a lot to the consumer.
C) the minimum number of defective items a consumer will accept in a lot.
D) none of the above.

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Multiple Choice

Q 22Q 22

A(n) ___ curve is a graph showing the probability of accepting a lot for different quality levels with a specific sampling plan.
A) operating characteristic (OC)
B) average outgoing quality
C) lot tolerance percent defective
D) single-sample attribute

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Q 23Q 23

Typically, the operating characteristic curve shows the following on the horizontal and vertical axis (answers are given as horizontal axis and vertical axis respectively):
A) proportion defective and probability of acceptance.
B) proportion non-defective and probability of acceptance.
C) proportion defective and probability of rejection.
D) proportion non-defective and probability of rejection.

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Q 24Q 24

The consumer's willingness to accept lots with a small proportion of defective items is known as the acceptable
A) sampling plan.
B) quality level.
C) consumer's risk.
D) producer's risk.

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Q 25Q 25

The ___ is the maximum number of defective items a customer will accept in a lot.
A) producer's risk
B) consumer's risk
C) average outgoing quality
D) lot tolerance percent defective

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Q 26Q 26

An operating characteristic (OC) curve is a graph that measures
A) the acceptable proportion of defects in a lot to the consumer.
B) the probability of accepting a lot for different quality levels with a specific sampling plan.
C) the probability of accepting a lot in which the fraction of defectives exceeds the lot tolerance percent defective.
D) the maximum number of defective items a consumer will accept in a lot.

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Multiple Choice

Q 27Q 27

The expected number of defective items that will pass on to the customer with a sampling plan is known as the
A) lot tolerance percent defective.
B) acceptable quality level.
C) average outgoing quality.
D) sampling plan.

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Multiple Choice

Q 28Q 28

The average outgoing quality is
A) the expected number of non-defective items that will pass on to the customer with a sampling plan.
B) the number of defective items in a lot that the customer is willing to accept.
C) the expected number of defective items that will pass on to the customer with a sampling plan.
D) the number of defective items in a lot that the customer is not willing to accept.

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Multiple Choice

Q 29Q 29

Which sampling plans are typically the least expensive?
A) single-sampling plans.
B) double -sampling plans.
C) multiple-sampling plans.
D) cannot be determined without further information.

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Q 33Q 33

Explain the basics of applying statistical process control (SPC) in production and services.

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Q 35Q 35

Use attribute control charts. The quality measures used in attribute control charts are discrete values reflecting a simple decision criterion such as good or bad.

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Q 36Q 36

Use variable control charts Variable control charts are used for continuous variables that can be measured, such as weight or volume.

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Q 39Q 39

Statistical process control involves monitoring and controlling a process to prevent poor quality.

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Q 40Q 40

Unique or special cause variation reflects the random variation associated with the output of a process.

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Q 41Q 41

Process control charts are rarely useful for monitoring and controlling the output of service processes.

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Q 43Q 43

Statistical process control is based on a philosophy of inspection as opposed to prevention.

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Q 44Q 44

One reason some companies fail in their attempt to apply statistical process control is lack of training.

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Q 45Q 45

One goal of statistical process control is to prevent a process from producing items that have to be scrapped or reworked.

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Q 46Q 46

Two types of variation associated with the output of a process are common (random) cause and special cause.

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Q 50Q 50

Employee training in statistical process control is a fundamental principle in total quality management programs.

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Q 53Q 53

After special cause variation is detected, the focus changes to identifying the root cause of the variation and eliminating it.

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Q 54Q 54

Process control is achieved by taking periodic samples from a process and plotting the sample points on a chart to determine if the process is within control limits.

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Q 57Q 57

Process control charts are often used at a critical point after which it is difficult to correct or rework the process output.

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Q 59Q 59

The individual that detects special cause variation in a process is not allowed to diagnose the root cause and correct it.

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Q 61Q 61

The formula used to determine the upper and lower control limits is based on specification limits.

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Q 62Q 62

When calculating control limits for a process, the number of standard deviations (z value) is typically six.

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Q 63Q 63

Control charts are never implemented until special cause variation has been detected in a process.

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Q 64Q 64

It is sometimes not necessary to determine new control limits after special cause variation has been identified if the source has been eliminated without changing the process.

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Q 65Q 65

When a control chart detects no special cause variation in a process, the upper and lower control limits are the same value.

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Q 66Q 66

When special cause variation is detected, it is normally eliminated by increasing the number of standard deviations (z value) used to calculate the control limits.

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Q 69Q 69

Attribute (qualitative) control charts are used to monitor descriptive characteristics of the output of a process.

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Q 72Q 72

The smaller the historical proportion defective reported for a process, the larger the sample size required to detect special cause variation with a p-chart.

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Q 74Q 74

When monitoring a process's output with a quantitative variable either an R-chart or an -chart is used, but never both.

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Q 75Q 75

Construction and use of an -chart is based on an assumption that the sample points are normally distributed around the centre line.

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Q 79Q 79

It is possible to have low variation within samples while at the same time having high variation between sample means.

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Q 80Q 80

Variable (quantitative) control charts are used to monitor measurable characteristics of a process's outputs.

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Q 84Q 84

In some cases, the -chart is used without the R-chart because within the sample variation is not of concern.

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Q 85Q 85

The process centre line for both and R-charts are both the same value because they are based on the same raw data.

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Q 86Q 86

In some cases, the -chart is used without an R-chart because there is no variation between the samples.

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Q 87Q 87

Statistical process control can prevent poor quality before it occurs if a pattern is evident in the plotted points.

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Q 89Q 89

A pattern test can identify an out-of-control process even if all sample points are within control limits.

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Q 92Q 92

If a pattern is evident in the points plotted on a control chart, the points are always considered evidence that the process is in control.

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Q 93Q 93

One advantage of using a pattern test is that special cause variations may be identified before any points are plotted outside the control limits.

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Q 94Q 94

Control chart sample sizes are becoming smaller because it is easier to detect a pattern with Excel or other data analysis software.

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Q 95Q 95

Using Excel to construct control charts should be avoided because most people believe using software results in too many errors.

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Q 97Q 97

The popularity of Excel and other data analysis software has been a major factor in the increased use of statistical process control.

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Q 100Q 100

Design specification limits should always be wider than the control limits for a given process.

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Q 101Q 101

The goal of statistical process control is to ensure that the control limits and specifications limits for a process always remain the same.

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Q 103Q 103

A process capability ratio greater than one shows that a process is capable of producing output within its specification limits.

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Q 104Q 104

A process capability ratio reflects the number of (Z) sigmas included in the range between the upper and lower control limits.

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Q 105Q 105

Some companies that strive to achieve extremely high quality use Z=6 (six sigma) vs. Z=3 (three sigma) when constructing control limits.

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Q 107Q 107

The process capability index is used only for p and c charts while the process capability ratio is used only for and R charts.

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Q 108Q 108

The process capability index indicates how much a process mean differs from the target specification value.

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Q 109Q 109

Excel can be used to increase the efficiency and accuracy of determining the process capability ratio and the process capability index.

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Q 110Q 110

Possible root causes of special cause variation include all of the following except
A) operator error.
B) process out of adjustments.
C) over producing.
D) defective materials.

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Q 111Q 111

Which of the following could a hospital be interested in observing
A) timeliness and quickness of care.
B) staff responses to requests.
C) accuracy of lab tests.
D) all of the above.

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Q 112Q 112

Which of the following is not a primary purpose of statistical process control?
A) to establish control limits
B) to detect special cause variations
C) to identify specification limits
D) to determine when a process is not in control

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Q 113Q 113

Four common types of control charts include all of the following except
A) -chart
B) t-chart
C) p-chart
D) c-chart

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Q 114Q 114

Which of the following is not a characteristic of a control chart?
A) The centre line is determined using special cause variations.
B) The upper and lower control limits are based on special cause variation.
C) The centre line is determined by using the target value.
D) None of the above are true.

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Multiple Choice

Q 115Q 115

Which of the following statements is true?
A) With wider control limits (larger Z), the process is more likely to be in control.
B) With narrower control limits, (smaller Z), the process is more likely to be in control.
C) With wider control limits (larger Z), the process is less likely to be in control.
D) None of the above are true.

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Q 116Q 116

Special cause variation in a process is more likely to be detected with
A) wider control limits.
B) narrow control limits.
C) wider specification limits.
D) narrow specification limits.

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Q 117Q 117

Which of the following statements concerning control chart limits is true?
A) The smaller the value of z, the more narrow the control limits are and the more sensitive the chart is to changes in the production process.
B) The larger the value of z, the more narrow the control limits are and the more sensitive the chart is to changes in the production process.
C) The smaller the value of z, the wider the control limits are and the less sensitive the chart is to changes in the production process.
D) The larger the value of z, the more narrow the control limits are and the less sensitive the chart is to changes in the production process.

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Multiple Choice

Q 118Q 118

After collecting a new sample and determining its average, which of the following should NOT be done?
A) Recalculate the control chart with the new information.
B) Plot the sample average into the existing control chart.
C) Check whether the new sample gives reason to believe that the process is not in control.
D) If the sample average is above the upper control limit, the process should be investigated.

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Q 119Q 119

A control chart that uses the actual number of defects per item to monitor a process is known as a
A) p-chart.
B) c-chart.
C) R-chart.
D) -chart.

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Multiple Choice

Q 120Q 120

If a sample of 40 units of output found 500 defects, then the centre line for monitoring the average number of defects per unit of output would be
A) = 40.
B) = 0.08.
C) = 12.5.
D) = 20,000.

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Multiple Choice

Q 121Q 121

If a sample of 40 units of output found 500 defects, then the 3-sigma upper control limit for the chart would be
A) 12.5.
B) 23.11.
C) 37.5.
D) 75.0.

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Q 122Q 122

A company randomly selects 100 light bulbs every day for 40 days from its production process. If 600 defective light bulbs are found in the sampled bulbs then the estimate for the process average defective would be
A) 6.667.
B) 0.167.
C) 0.150.
D) 0.250.

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Q 123Q 123

A company randomly selects 100 light bulbs every day for 40 days from its production process. If 600 defective light bulbs are found in the sampled bulbs then the 3-sigma lower control limit would be
A) 0.0357.
B) 0.00.
C) 0.15.
D) -1.0119.

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Q 124Q 124

To monitor the number of blemishes on a polished surface, a company randomly selects 10 units of output from its process and counts the number of blemishes on each unit. The sample results are shown below: Given the sample information above, the average number of defects per unit for this process would be
A) 160.
B) 80.
C) 16.
D) 10.

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Q 125Q 125

To monitor the number of blemishes on a polished surface, a company randomly selects 10 units of output from its process and counts the number of blemishes on each unit. The sample results are shown below: Given the sample information above, the standard deviation of the number of defects for this process would be
A) 16.
B) 10.
C) 1.56.
D) 0.

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Q 126Q 126

Which of the following control charts is based on the number of defects within a sample?
A)
B) R
C) c
D) p

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Q 127Q 127

Which of the following control charts is used to monitor the proportion of defective items within a sample?
A)
B) R
C) c
D) p

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Q 128Q 128

If the quality of a process's output is determined by the number of defects within a small sample, use a(n) ___ control chart.
A)
B) R
C) c
D) p

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Q 129Q 129

If the quality of a process's output is determined by classifying the output as being defective or not defective, use a(n) ___ control chart.
A)
B) R
C) c
D) p

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Q 130Q 130

Which of the following control charts are based on sample sizes as small as one?
A)
B) R
C) c
D) p

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Q 131Q 131

Which of the following control charts are often based on sample sizes larger than one hundred?
A)
B) R
C) c
D) p

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Q 132Q 132

Consider the number of patient falls per day in a hospital. Which of the following control charts is most applicable in this case?
A)
B) R
C) c
D) p

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Q 133Q 133

A control chart that reflects the amount of dispersion, or spread, present within each sample is known as a(n)
A) p-chart
B) c-chart
C) R-chart
D) -chart

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Q 134Q 134

If the quality of a process's output is determined by the difference between the largest and smallest values in a sample, use a(n) ___ control chart.
A)
B) R
C) c
D) p

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Q 135Q 135

If the quality of a process's output is determined by the average value of a sample, use a(n) ___ control chart.
A)
B) R
C) c
D) p

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Q 136Q 136

Which of the following control charts is used to control the variation within samples?
A)
B) R
C) c
D) p

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Q 137Q 137

Which of the following control charts is used to control the variation between samples?
A)
B) R
C) c
D) p

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Q 138Q 138

Which of the following charts are frequently used together to monitor and control quality?
A) p and
B) R and p
C) c and R
D) R and

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Q 139Q 139

If ?σ is the population standard deviation, k the number of samples or subgroups, and n the sample size (number of observations in each subgroup), what is the distance from the centre line to the upper control limit?
A) σ
B) 3 σ
C) 3 σ / √k
D) 3 σ / √n

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Q 140Q 140

In general, a process is considered to be in control for all the following conditions except
A) no points are outside the control limits.
B) all points are significantly above the centre line.
C) the points are randomly distributed following a normal population.
D) no pattern exists in the plotted points (no evidence of a run).

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Multiple Choice

Q 141Q 141

There are several general guidelines associated with the zones for identifying patterns in a control chart, where none of the observations are beyond the control limits. Which of the following is NOT one of those guidelines?
A) Fourteen points alternating up or down.
B) Two out of three consecutive points in Zone A (on one side of the centre line).
C) Three out of four consecutive points in Zone B (on one side of the centre line).
D) Four out of five consecutive points in Zone A or B (on one side of the centre line)

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Q 142Q 142

A process is generally considered to be in control when
A) there are no sample points outside the control limits.
B) most points are near the centre line, without many being close to the control limits.
C) sample points are randomly distributed equally above and below the centre line.
D) all of the above are true.

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Q 143Q 143

For the process to be capable of meeting design specification, the process capability index must be
A) less than one (1.0).
B) equal to or greater than one (1.0).
C) smaller than Six Sigma.
D) larger than Six Sigma.

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Multiple Choice

Q 144Q 144

A company produces a product which is designed to weigh 10 oz., with a tolerance of + 0.5 oz. The process produces products with an average weight of 9.95 oz. and a standard deviation of 0.10 oz. The process capability ratio for this process is
A) 1.67.
B) 0.
C) 0.8333.
D) -1.67.

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Q 145Q 145

A company produces a product which is designed to weigh 10 oz., with a tolerance of + 0.5 oz. The process produces products with an average weight of 9.95 oz. and a standard deviation of 0.10 oz. According to the process capability ratio, is the process capable of meeting design specifications?
A) No, the process capability ratio is less than 1.0.
B) Yes, the process capability ratio is less than 1.0.
C) No, the process capability ratio is greater than 1.0.
D) Yes, the process capability ratio is greater than 1.0.

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Q 146Q 146

A company produces a product which is designed to weigh 10 oz., with a tolerance of + 0.5 oz. The process produces products with an average weight of 9.95 oz. and a standard deviation of 0.10 oz. The process capability index for this process, with z = 3, is
A) 1.50.
B) -1.50.
C) 1.83.
D) -1.83.

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Q 147Q 147

A company produces a product which is designed to weigh 10 oz., with a tolerance of + 0.5 oz. The process produces products with an average weight of 9.95 oz. and a standard deviation of 0.10 oz. According to the process capability index
A) the process mean is off centre and most of the items are defective.
B) the process is capable of meeting design specifications.
C) the process mean is centred on the design target.
D) none of the above.

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Q 148Q 148

A company manufactures a product that has a design (nominal) target width of 5 inches with tolerances of + .05 inch. The process that produces the product has a mean of 4.995 inches and a standard deviation of 0.01 inch. The process capability ratio for this process is
A) -1.67.
B) -1.5.
C) 1.5.
D) 1.67.

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Multiple Choice

Q 149Q 149

A company manufactures a product that has a design (nominal) target width of 5 inches with tolerances of + .05 inch. The process that produces the product has a mean of 4.995 inches and a standard deviation of 0.01 inch. The process capability index for this process is
A) 1.67.
B) 1.5.
C) -1.5.
D) -1.67.

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Q 150Q 150

Assume that a process is operating on target and 99.8% of the products manufactured just fit within the specification limits. What can you say about the process?
A) The process is not capable.
B) The process is just capable.
C) The process is highly capable.
D) The process is world-class capable.

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