SEEM3500: Quality Control and Management
Quality Control and Management
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SEEM3500: Quality Control and Management
Mid-term Exam
This exam paper has three parts. Part I has 10 questions, Part II has 5 questions and Part III
has 4 questions. Do all of the questions. The total mark is 100. Three notes are attached to the
exam paper: Control chart constants, seven rules to detect out-of-control points and table of
standard normal distribution. Minitab data files must be downloaded separately from the same
website of this exam paper on Blackboard.
PART I --- True/False (15 marks = 1.5 marks each × 10)
Read the following statements and mark them either True or False for each of the statements.
1) A product exhibiting high quality of performance must have high degree of uniformity
and dependability.
2) Both quality of design and ideas for innovation come from customer’s needs
3) A product with defects is nonconforming.
4) Quality control is mainly concerned with quality of conformance.
5) S-chart is used to reduce the impact of extreme values in each subgroup on the variability
of the subgroup statistics.
6) Out-of-control patterns in a p-chart are identical to the out-of-control patterns in the
associated np-chart.
7) Control charts are designed on the assumption that the data are truly random. Out-of-
control patterns identify some of the data points in a control chart which do not display
the expected random nature.
8) From quality consciousness perspective, attribute control charts are mainly used for
defective prevention whereas variables control charts are used for further improvement
of process.
9) Using median instead of average in plotting I-MR chart is to reduce the effects from
extreme data.
10) Quality control is completed once all special causes of variation are fixed and the process
is stabilized.
PART II --- Explanation (20 marks = 5 marks each × 4)
1) Explain briefly the difference between variance of individual units and variance of
subgroup statistic.
2) Explain similarity and difference between p-chart and u-chart.
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3) Estimate the proportion of data falling in zone B in a stable process and explain why.
4) Explain briefly the difference between customer specification limits and upper lower
control limits of a control chart.
5) Explain briefly the similarity and difference between histogram and bar chart.
PART III --- Calculation (65 marks)
1. (17 marks) A large publisher counts the number of keyboard errors that make their way
into finished books. The number of errors and the number of pages in the past 26
publications are (see BOOK ):
(a) (5 marks) Construct a control chart for these data.
(b) (5 marks) Are there any indications of a lack of control? For which books?
(c) (7 marks) Reconstruct the control chart after removing all data points which go
beyond the control limits. Is the control chart stable? Why?
2. (13 marks) A firm manufactures high-voltage capacitor film for the electronics industry.
They are concerned with the yield on a slitter process that produces reels of film. Reels
that are nonconforming must be scrapped. Reels were sampled and inspected each week
for 30 weeks (see REELS). The number of reels of film in each sample, number of scrap
reels, and proportion of scrap reels are as follows:
(a) (7 marks) Construct an appropriate control chart.
(b) (6 marks) Is the process in a state of control? Why?
3. (20 marks) The house keeping staff in a large resort hotel cleans and prepares all of the
guest-rooms daily. In an effort to improve service through reducing variation in the time
required to clean and prepare a room, a series of measurements is taken of the times to
service rooms in one section of the hotel. The cleaning times for five rooms for 25
consecutive days are recorded in minutes in the Minitab file HOTEL.
(a) (5 marks) Construct an appropriate control chart for the data using the measurements
of five rooms each day as subgroup. Discuss your findings.
(b) (8 marks) Construct a proper control chart for the data using the measurements of
five consecutive days of each room as a subgroup. Discuss your findings. Hint: sort
out the data in the order of room and day first and then do further sorting.
(c) (7 marks) Construct a control chart for each room with subgroup size of 5 and discuss
your findings.
4. (15 marks) A small independent public water utility in the San Francisco area monitored
daily usage of water (1 unit = 748,000 gallons) for a period of 10 weeks (Monday to
Friday only) during September, October and November in a recent year. See WATER
for the data. Records show that on day 5 a water main broke and a major leak occurred.
No other anomalies were recorded.
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(a) (5 marks) Construct an appropriate control chart for the given data. Is the process in
control? When does out-of-control behaviour occur?
(b) (10 marks) Use proper formulae to compute the upper control limit and upper zone
boundary between zone A and zone B after the control chart is stabilized and compare
your answers with the results from Minitab.