OPERATIONS MANAGEMENT – PROBLEMS IN – Statistical Quality Control
Chapter 6. Statistical Quality Control
Question 1 
A quality control manager at a manufacturing facility has taken four samples with four observations each of the diameter of a part.
Samples of Part Diameter in Inches
1  2  3  4  
6.2  5.8  5.7  5.8  
6.2  6.3  6.1  6.1  
6.0  5.9  6.2  6.1  
5.9  5.7  5.9  6.2 
(a) Compute the mean of each sample. (Round answers to 3 decimal places, e.g. 15.250.)
Mean of sample 1  
Mean of sample 2  
Mean of sample 3  
Mean of sample 4 
(b) Compute an estimate of the mean and standard deviation of the sampling distribution. (Round answers to 4 decimal places, e.g. 15.2500.)
Mean  
Standard deviation 
(c) Develop control limits for 3 standard deviations of the product diameter. (Round answers to 2 decimal places, e.g. 15.25.)
CL  
UCL  
LCL 



Question 3 
A production manager at a Contour Manufacturing plant has inspected the number of defective plastic molds in five random samples of 35 observations each. Following are the number of defective molds found in each sample:
Sample  Number of Defects  Number of Observations in Sample  
1  3  35  
2  2  35  
3  0  35  
4  1  35  
5  0  35  
Total  6  175 
Construct a 3sigma control chart (z = 3) with this information. (If the lower control limit is negative, round the LCL to zero and all other answers to 2 decimal places, e.g. 15.25.)
CL  
UCL  
LCL 
Question 4 
Ulearn University uses a cchart to monitor student complaints per week. Complaints have been recorded over the past ten weeks. Develop 3sigma control limits using the following data:
Week  Number of Complaints  
1  0  
2  2  
3  1  
4  2  
5  2  
6  3  
7  3  
8  0  
9  3  
10  3 
(If the lower control limit is negative, round the LCL to zero and all other answers to 2 decimal places, e.g. 15.25.)
CL  
UCL  
LCL 




Question 6 
Compute the (a) Cpk and (b) Cp measures of process capability for the following machine. (Round answers to 2 decimal places, e.g. 15.25.)
Machine data:  USL = 100  
LSL = 70  
Process σ = 5  
Process μ = 80 
Cpk  
Cp 






Question 9 
The Crunchy Potato Chip Company packages potato chips in a process designed for 8.0 ounces of chips with an upper specification limit of 8.5 ounces and a lower specification limit of 7.5 ounces. The packaging process results in bags with an average net weight of 7.86 ounces and a standard deviation of 0.1 ounces. The company wants to determine if the process is capable of meeting design specifications. (Round answers to 3 decimal places, e.g. 15.250.)
Cp  
Cpk 
The process is .
Question 1 
Discuss the key differences between common and assignable causes of variation. Give examples.
Question 2 
The standard deviation of the distribution of sample means is computed by
z*σ 
σ/z 
σ/x 
σ/√n 
Question 3 
For the standard normal distribution, how much confidence is provided within 2 standard deviations above and below the mean?
97.22% 
95.44% 
99.74% 
99.87% 
90.00% 
Question 4 
SixSigma quality implies how many average defects per million?
3.4 
6 
2600 
3σ 
6σ 
Question 5 
A control chart for ______________ is used to monitor characteristics that can be measured.
data 
attributes 
variables 
limits 
deviations 
Question 6 
A control chart for ______________ is used to monitor characteristics that have discrete values and can be counted.
data 
attributes 
variables 
deviations 
limits 