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Exam 19: Statistical Process Control

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Question 21

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For a 3-sigma x-bar chart where the process standard deviation is known,the upper control limit:

A) is 3σ below the mean of sample means for a 3σ control chart.
B) is 3σ above the mean of sample means for a 3σ control chart.
C) is 3σ/ below the mean of sample means for a 3σ control chart.
D) is 3σ/ above the mean of sample means for a 3σ control chart.
E) cannot be calculated unless the average range is known.

F) B) and D)
G) A) and B)

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Question 22

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Repeated sampling of a certain process shows the average of all sample ranges to be 1.0 cm.The sample size has been constant at n = 5.What are the 3-sigma control limits for this R-chart?

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LCL = 0,an...

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Question 23

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Acceptance sampling accepts or rejects an entire lot based on the information contained in the sample.

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

A process range chart illustrates the amount of dispersion within the samples.

An operating characteristics curve shows:

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

If μ = 9 ounces,σ = 0.5 ounces,and n = 9,calculate the 3-sigma control limits for the x-bar chart.

A hospital-billing auditor has been inspecting patient bills.While almost all bills contain some errors,the auditor is looking now for large errors (errors in excess of $250).Each day last week,the auditor examined 100 bills and found an average defect rate of 16%.Calculate the upper and lower limits for the billing process for 99.73% confidence.

When a lot has been accepted by acceptance sampling,we know that:

A local manufacturer supplies you with parts,and you would like to install a quality monitoring system at his factory for these parts.Historically,the defect rate for these parts has been 1.25 percent (You've observed this from your acceptance sampling procedures,which you would like to discontinue).Develop ± 3σ control limits for this process.Assume the sample size will be 200 items.

Natural variations:

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

Ten samples of size four were taken from a process,and their weights measured.The sample averages and sample ranges are in the following table.Construct and plot an x-bar and R-chart using these data.Is the process in control?

Assignable causes:

A process that is in statistical control will always yield products that meet their design specifications.

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?

Assignable variation:

A woodworker is concerned about the quality of the finished appearance of her work.In sampling units of a split-willow hand-woven basket,she has found the following number of finish defects in ten units sampled: 4,0,3,1,2,0,1,2,0,2. a.Calculate the average number of defects per basket. b.If 3-sigma control limits are used,calculate the lower control limit and upper control limit.

The x-bar chart,like the c-chart,is based on the exponential distribution.