Chapter 9 questions – 327

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Read Chapter 9 (Schoeder, R.G., Goldstein, S.M., & Rungtusanatham, M.J. (2013). Operations Management in the Supply Chain: Decisions and Cases (6th Ed). McGraw-Hill Irwin, New York, NY ISBN: 978-0-07-352524-2) and create a Microsoft Word document with your responses to the following questions.

Q1: Golden Gopher Airline issues thousands of aircraft boarding passes to passengers each day. In some cases, a boarding pass is spoiled for various reasons and discarded by the airline agent before the final boarding pass is issued to a customer. To control the process for issuing boarding passes, the airline has sampled the process for 100 days and determined the average proportion of defective passes is .006 (6 in every 1000 passes are spoiled and discarded). In the future, the airline plans to take a sample of 500 passes that are issued each day and calculate the proportion of spoiled passes in that sample for control chart purposes.


  • A. What is the sample size (n) for this problem? Is it 100, 500, or 1000? Explain the significance of the 100 days used to determine the average proportion defective. 
  • B. Calculate the CL, UCL, and LCL, using three standard deviations for control purposes.

Q2: We have taken 12 samples of 400 letters each from a typing pool and found the following proportions of defective letters: .01, .02, .02, .00, .01, .03, .02, .01, .00, .04, .03, and .02. A letter is considered defective when one or more errors are detected.

  • A. Calculate the control limits for a p control chart. 
  • B. A sample of 400 has just been taken, and 6 letters were found to be defective. Is the process still in control?  

 Q3: Each day 500 inventory control records are cycle-counted for errors. These counts have been made over a period of 20 days and have resulted in the following proportion of records found in error each day:
.0025, .0075, .0050, .0150, .0125, .0100, .0050, .0025, .0175, .0200, .0150, .0050, .0150, .0125, .0075, .0150, .0250, .0125, .0075, .0100

  • A. Calculate the center line, upper control limit, and lower control limit for a p control chart. 
  • B. Plot the 20 points on the chart and determine which ones are in control. 
  • C. Is the process stable enough to begin using these data for quality control purposes? 


 Q9: The Robin Hood Bank has noticed an apparent recent decline in the daily demand deposits. The average daily demand deposit balance has been running at $109 million with an average range of $15 million over the past year. The demand deposits for the past six days have been 110, 102, 96, 87, 115, and 106.

  • A. What are the CL, UCL, and LCL for the x and R charts based on a sample size of 6?
  • B. Compute an average and range for the past six days. Do the figures for the past six days suggest a change in the average or range from the past year? 



As cereal boxes are filled in a factory; they are weighed for their contents by an automatic scale. The target value is to put 10 ounces of cereal in each box. Twenty samples of three boxes each have been weighed for quality control purposes. The fill weight for each box is shown below.

a. Calculate the center line and control limits for the x and R charts from these data.

b. Plot each of the 20 samples on the x and R control charts and determine which samples are out of control. 

c. Do you think the process is stable enough to begin to use these data as a basis for calculating 

 x and R and to begin to take periodic samples of 3 for quality control purposes?