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Exam 15: Statistical Quality Control

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Question 61

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As a rule of thumb,operations with a high proportion of human involvement necessitate less inspection than mechanical operations,which tend to be less reliable.

A) True
B) False

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Question 62

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

A) True
B) False

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Question 63

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A control chart used to monitor the number of defects per unit is the:

Given the following process control data for a normally distributed quality variable (three samples of size four each): If the process is known to have a mean of 15 and a standard deviation of 3,using three sigma control limits,do any of the sample means indicate an out-of-control process mean?

A Quality Analyst wants to construct a control chart for determining whether four machines,all producing the same product,are under control with regard to a particular quality attribute.Accordingly,she inspected 1,000 units of output from each machine in random samples,with the following results: If upper and lower control limits were set as 0.028 and 0.010,which machine(s) ,if any,appear(s) to be out-of-control for process proportion of defectives?

The primary purpose of statistical process control is to detect defects in finished products before they are shipped to customers.

The process capability index,indicated by Cpk is used only when the process is centred.

A c-chart is used for:

A control chart used to monitor the fraction of defectives generated by a process is the:

The Chair of the Operations Management Department at Quality University wants to construct a p-chart for determining whether the four instructors teaching the basic P/OM course are under control with regard to the number of students who fail the course.Accordingly,he sampled 100 final grades from last year for each instructor,with the following results: What are the .95 (5% alpha risk) upper and lower control limits for the p-chart?

Given the following process control data for a normally distributed quality variable (three samples of size four each): If the process is known to have a mean of 15 and a standard deviation of 3,what is the alpha risk (probability of Type I error)for upper and lower control limits of 16.5 and 13.5 respectively? 18 and 12? 19.5 and 10.5?

Given the following process control data for a quality attribute (three samples of size 400 each): If the process is known to produce 11 percent defectives on average,what is the mean of the sampling distribution of sample proportions for whenever this process is under control? The standard deviation?

Given the following process control data for a quality attribute (three samples of size 400 each): If the process proportion of defectives is unknown,what is the estimate of it?

What should managers have in place if a point is observed that is outside the control limits,or a run test produces a large z-value?

Concluding that a process has changed when it has not is known as a Type I error.

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

The probability of concluding that an assignable variation exists when only random variation is present is:

A design engineer wants to construct a sample mean chart for controlling the service life of one of the types of light bulbs his company produces.He knows from numerous previous samples that this service life is normally distributed with a mean of 500 hours and a standard deviation of 20 hours.On three recent production batches,he tested service life on random samples of four bulbs,with these results: What value should be used as the mean of the sampling distribution of sample means?

A point which is outside of the lower control limit on an R-chart:

A Quality Analyst wants to construct a control chart for determining whether three machines,all producing the same product,are under control with regard to a particular quality variable.Accordingly,he sampled four units of output from each machine,with the following results: What is the sample average range based upon this limited sample?