Exam 10: Quality Control

A design engineer wants to construct a sample mean chart for controlling the service life of a halogen headlamp his company produces. He knows from numerous previous samples that when this service life is in control it 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 headlamps, with these results What is the mean of the sampling distribution of sample means when the service life is in control?

This step in the control process includes characteristics that can be counted.

A quality analyst wants to construct a sample mean chart for controlling a packaging process. He knows from past experience that whenever this process is in control, package weight is normally distributed with a mean of 20 ounces and a standard deviation of two ounces. Each day last week, he randomly selected four packages and weighed each What is the standard deviation of the sampling distribution of sample means for whenever this process is in control?

A quality analyst wants to construct a control chart for determining whether four machines, all producing the same product, are in 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 What are the control chart upper and lower control limits for an alpha risk of .05?

Patterns of data on a control chart suggest that the process may have nonrandom variation.

A c-chart is used for

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 1-inch pipe has a specification of 1 inch plus or minus 0.10 inch. What is the process capability index ( C_pk)if the long-run process mean is 1 inch?

Control limits tend to be wider for more variable processes.

Statistical process control focuses on the acceptability of process output.

The chair of the operations management department at Quality University wants to construct a p-chart for determining whether the four faculty teaching the basic P/OM course are in 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 Using .95 control limits (5 percent risk of Type I error), which instructor(s), if any, should he conclude is (are)out of control?

A quality analyst wants to construct a control chart for determining whether three machines, all producing the same product, are in control with regard to a particular quality variable. Accordingly, he sampled four units of output from each machine, with the following results For upper and lower control limits of 23.29 and 16.71, which machine(s), if any, appear(s)to have an out-of-control process mean?

Range control charts are used to monitor process central tendency.

A quality analyst wants to construct a control chart for determining whether four machines, all producing the same product, are in 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 What is the sample proportion of defectives for machine #1?

This step in the control process includes a definition of out of control.

A quality analyst wants to construct a control chart for determining whether four machines, all producing the same product, are in 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 What is the estimate of the standard deviation of the sampling distribution of sample proportions for this process?

Which of the following relationships must always be incorrect?

A run test checks a sequence of observations for randomness.

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.

Attribute data are counted, variable data are measured.

A quality analyst wants to construct a control chart for determining whether three machines, all producing the same product, are in control with regard to a particular quality variable. Accordingly, he sampled four units of output from each machine, with the following results What are the x-bar chart three-sigma upper and lower control limits?