Exam 19: Statistical Methods for Quality Control

The quality control department of a company has decided to select a sample of 20 items from each shipment of goods it receives and inspect them for defects. It has been decided that if the sample contains no defective parts, the entire lot will be accepted. Each shipment contains 1,000 items. a.What is the probability of accepting a lot that contains 10% defective items? b.What is the probability of accepting a lot that contains 5% defective items? c.What is the probability of rejecting a lot that contains 15% defective items?

A control chart that is used to monitor the range of the measurements in a sample is

A statistical procedure in which the number of defective items found in a sample is used to determine whether a lot should be accepted or rejected is called

The process mean and standard deviation can be estimated by using samples that are selected from the process when

A control chart that is used to monitor the number of defectives in a sample is

Snipper, Inc. manufactures lawnmowers that require minor, final assembly by the customer. A sealed plastic bag containing the hardware (nuts, bolts, washers, and so on) needed for final assembly is included with each lawnmower shipped. During a week of normal, in-control operation, twenty samples of 200 bags of hardware were examined for content (hardware type and count) accuracy. A total of 104 bags of the 4000 examined failed to have the correct contents. a. Compute the upper limit, center line, and lower limit for a p chart. b. Compute the upper limit, center line, and lower limit for an np chart.

A control chart that is used when the output of a production process is measured in terms of the proportion defective is

Six Sigma represents a quality level of at most ____ defects per million opportunities.

Jane Hotchkiss, director of production at the center, has decided to record the number of defective labels in random daily samples on control charts. Jane estimates that 1.5 percent loose labels is typical when the labeling process is in control.Twelve daily samples, each consisting of 200 pairs of jeans, were selected and examined. The number of defective labels found in each sample is shown below. a. Determine the center line and the 3 $\sigma$ control limits for the p chart. b. Decide if the labeling operation is in control.

We can examine the effect of the sampling plan on both types of risks by varying the assumed

Accepting a good-quality lot would be a

A production process is considered in control if 6% of the items produced are defective. Samples of size 300 are used for the inspection process. a.Determine the standard error of the proportion. b.Determine the upper and the lower control limits for the p chart.

The following data represent the filling weights based on samples of 350-gram containers. Ten samples of size 5 were taken. Use Excel to develop an x-bar chart.

Five samples were taken, with five observations each. The sample findings are listed below. The sample values represent service times in minutes. a. Determine the control limits for the R-chart. b. Would you conclude the R-chart is in statistical control and proceed to develop the x-bar chart?

A production process that is in control has a mean ( $\mu$ ) of 80 and a standard deviation ( $\sigma$ ) of 10. a.Determine the upper and the lower control limits for sample sizes of 25. b.Five samples had means of 81, 84, 75, 83, and 79. Construct an x-bar chart and explain whether or not the process is in control.

The general practice in quality control is to set the control chart's upper and lower control limit values equal to the variable's mean value +/-

A control chart used when the output of a process is measured in terms of the mean value of a variable such as a length, weight, temperature, and so on is

Variation in the quality of production output that is due to factors such as machine tools wearing out is called

A group of items such as incoming shipments of raw material is called

If the value of c in a single-stage sampling plan is increased, with n remaining constant, the probability of accepting the lot