# Statistical Quality Control Questions and Answers – Attribute Charts – Control Charts for Nonconformities (Defects) – 3

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This set of Statistical Quality Control Multiple Choice Questions & Answers (MCQs) focuses on “Attribute Charts – Control Charts for Nonconformities (Defects) – 3”.

1. If there is variable sample size to be used with the u-chart or average number of nonconformity per unit chart, which of these methods, is used?
a) DMAIC
b) Designing of Experiments
c) Acceptance sampling
d) Standardized control chart

Explanation: When the sample size is variable, for a u-chart, the method of using the standardized chart is used to deal with the variable sample size. This makes it easy to use all the sample size data with the nonconformity data.

2. The method of average sample size is used when there is _____
a) Variable sample size
b) Constant sample size
c) Sample size=1
d) Sample Size=10

Explanation: When the sample size is variable and the u-chart or the control chart for nonconformity data is to be used, the approach of average sample size is used.

3. In the average sample size approach to design u-chart with variable sample size, which of these is used to calculate the average sample size?
a) $$\bar{n}=\frac{\sum_{i=0}^m n_i}{m}$$
b) $$\bar{n}=\frac{\sum_{i=1}^m u_i}{2m}$$
c) $$\bar{n}=\frac{\sum_{i=1}^m n_i}{m}$$
d) $$\bar{n}=\frac{\sum_{i=1}^n u_i}{m}$$

Explanation: The average sample size for the u-chart with variable sample size is calculated using the following formula,
$$\bar{n}=\frac{\sum_{i=1}^m n_i}{m}$$

4. In a demerit system for defects, how many classes are defined for defects to be classified?
a) 3
b) 4
c) 5
d) 8

Explanation: The demerit system for attribute data; classifies the defects in 4 classes; class A, class B, Class C, and Class D.

5. Serious defects are put into which class according to the Demerit system for attribute data?
a) Class C
b) Class D
c) Class A
d) Class B

Explanation: Serious Defects are put into the class B. In serious defects reduce the effective life of the component or increase the maintenance costs to be applied for the use of that component.

6. The Class A defects are ____________
a) Moderate
b) Minor
c) Serious
d) Very Serious

Explanation: The class A defects contains all the defects which are very serious to be present in the part. These defects either make the part totally unfit for use or will fail in service causing property damage with it.

7. The minor defects are put into class ____________ of the demerit system.
a) A
b) B
c) C
d) D

Explanation: The minor defects are the defects which do not affect the service of part effectively. They are classified in the Class D of the Demerit system for attribute data.

8. The minor finish, appearance, or quality of work defects are generally classified in _____ of the demerit system.
a) Class A
b) Class D
c) Class C
d) Class B

Explanation: The minor defects in finish, quality of work, and appearance are generally not serious. They do not affect the life of product effectively. So they are classified into class D of the demerit system.

9. Moderate defects are classified into which class of demerit system?
a) Class B
b) Class C
c) Class D
d) Class A

Explanation: The moderate defects are the defects which cause trouble that is less serious than operating failure.

10. The number of demerits in a system having ciA,ciB,ciC,and ciD defects in classes A, B, C, and D respectively is expressed by ______ It is assumed that the probability of each defect varies according to a Poisson distribution.
a) di = 100ciD + 50ciB + 10ciC + ciA
b) di = 100ciA + 50ciB + 10ciC + ciD
c) di = 100ciB + 50ciA + 10ciC + ciD
d) di = 100ciA + 50ciC + 10ciB + ciD

Explanation: The number of demerits in a system is expressed by the following expression.
di = 100ciA + 50ciB + 10ciC + ciD.

11. If there are 8, 12, 11, 3, 6 demerits in sample number 1, 2, 3, 4, and 5 respectively, what will be the demerits per units for the mentioned output?
a) 8
b) 11
c) 3
d) 5

Explanation: The demerits per unit are calculated by using the following formula,
$$u_i=\frac{D}{n}$$
Where D=$$\sum_{i=1}^n d_i$$ = 40 and n=5. We get ui=8

12. The upper control limit for the demerits per unit chart is given by _____
a) UCL = $$\bar{u}-3\widehat{σ_u}$$
b) UCL = $$\bar{u}+3\widehat{σ_u}$$
c) UCL = $$\bar{u}+\widehat{σ_u}$$
d) UCL = $$\bar{u}-\widehat{σ_u}$$

Explanation: The upper control limit for the demerits per unit chart is given by the following formula,
UCL = $$\bar{u}+3\widehat{σ_u}$$
Where $$\bar{u}=100\overline{u_A}+50\overline{u_B}+10\overline{u_C}+\overline{u_D}$$

13. What is the value of the center line of the demerits per unit?
a) $$\bar{u}+3\sqrt{\bar{u}}$$
b) $$\bar{u}$$
c) $$\bar{u}+\frac{1}{2}\sqrt{\bar{u}}$$
d) $$\bar{u}-3\sqrt{\bar{u}}$$

Explanation: The value of the center line of the demerits per unit chart is given by,
CL = u

14. A serious defect is defined as the defect which makes the unit totally unfit for use.
a) True
b) False

Explanation: The defect which makes the unit totally unfit for use, is called a very serious defect, and it is categorized in Class A demerit of the demerit system of the attribute data.

15. For construction of the control charts for nonconformities, the inspection unit must be same for each sample.
a) True
b) False

Explanation: It is necessary that the inspection unit must be same for each sample for the construction of the control chart for nonconformities. Thus, there will be a same area of opportunity for the occurrence of nonconformities for each inspection unit.

16. The defects which affect the proper working of the unit in the service arena, are called ____________
a) Appearance Defects
b) Functional Defects
c) Specification Defects
d) Aspect defects 