Question 1
“There is no need of revision of control limits once calculated by the equations of control limits.
A. TRUE
B. FALSE
View Answer
Answer: Option B
Explanation:
In the phase I application of control charts, the limits calculated from equations are used as trial limits because it gives us an idea about the variation, both, inherent and natural. So with time the variation changes, to compensate this, limits must be revised after a certain time.
Question 2
A mixture pattern in the control chart points is exhibited when __________ occurs.
A. Operator fatigue
B. Change of raw materials
C. Continuous wear of tool
D. Adjustments too often responding to random variation
View Answer
Answer: Option D
Explanation:
When the “Over-control” occurs, i.e. the operator adjusts the processes very frequently and recurrently, the random pattern of the process data vanishes and a mixed pattern is obtained.
Question 3
A permanent change in the sample size is made only because of cost or because has exhibited good stability and fewer resources are allocated for process monitoring.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The permanent change in sample size is not a frequent activity. So it is done because of some major reasons like cost or extraordinary good performance of process on control chart.
Question 4
A single measureable quality characteristic, such as dimension, weight, or volume, is called ________
A. Variable
B. Attribute
C. Variable and an Attribute
D. Mean and variablility
View Answer
Answer: Option A
Explanation:
A single measurable quality characteristic is that CTQ that can be measured on a continuous scale. So it is also called a variable, be it a dimension or a weight measurement of a product unit.
Question 5
A tolerance diagram is also called ____________
A. Scatter diagram
B. Defect concentration diagram
C. Histogram
D. Tier chart
View Answer
Answer: Option D
Explanation:
The run chart of individual observations in each sample is called the tolerance diagram for any process. The tolerance diagram is also called Tier chart of the process.
Question 6
A variable quality characteristic will have both __________
A. Mean and variability
B. Discrete and continuous values
C. Zero and infinite value
D. One or zero
View Answer
Answer: Option A
Explanation:
A variable quality characteristic will vary on a continuous scale. So it will have both, a mean and its variability.
Question 7
Control limits are ___________
A. Limits defined by customers
B. Limits driven by the natural variability of the process
C. Limits driven by the inherent variability of the process
D. Statistical limits
View Answer
Answer: Option B
Explanation:
The control limits are the limits for a quality characteristic for a process to be in-control. They are driven by the natural variability of the process.
Question 8
Control of the process average or mean quality level is usually done with the ___________ control chart.
A. X bar control chart
B. S control chart
C. R chart
D. P chart
View Answer
Answer: Option A
Explanation:
If a quality characteristic has a mean and variability, it is called a variable. If the control of process average or mean quality level is to be done for a variable, an x bar variable control chart is used.
Question 9
For a random variable having a normal distribution, the ratio of its range to the standard deviation is called ____________
A. Relative range
B. Absolute range
C. Major range
D. Minor range
View Answer
Answer: Option A
Explanation:
For a normal random variable, the ratio of its range to the standard deviation is called the relative range for that random variable.
Question 10
For any process, the sample ranges are, 1.2,1.5,1.1,1.4,1.5. The subgroup size is 5. What will be the process standard deviation? Given: d2=2.326 and A2=0.577
A. 0.576
B. 2.322
C. 0.511
D. 2.463
View Answer
Answer: Option A
Explanation:
We know that,\(\bar{R} = \frac{\sum_{i=0}^{i=n} R_i}{n}\) and “process standard deviation = \(\frac{\bar{R}}{d_2}\)“, by using the values of R and d2 in the question, we get process standard deviation=0.576
Question 11
For standard values of mean and standard deviation used, what does the center line of the R chart represent?
A. R bar
B. d2 σ
C. D2 σ
D. d2 R
View Answer
Answer: Option B
Explanation:
For the standard values of mean and standard deviation used, the center line for a R chart is determined by the following formula, d2 σ.
Question 12
If a process is said to be in control, what can we say about the variation?
A. Random
B. Normal
C. Attribute
D. Assignable
View Answer
Answer: Option A
Explanation:
If a process is said to be in control, its sample data will have a random pattern. So when plotted on a control chart, they will appear to have a random distribution.
Question 13
If the means for sample 1 to 4 for a process are, 12.67, 22.32, 14.53, 12.11; what value will be the center line of x chart indicating?
A. 15.2
B. 15.4
C. 14.8
D. 14.9
View Answer
Answer: Option B
Explanation:
The center line of the x chart, indicates the mean of all means of samples; i.e.,CL=\(\bar{\bar{x}} = \frac{\sum \bar{x}}{N}\)=15.4
Question 14
If the sample size is 7 and the Average run length is 122 for a process, what will be the expected number of the individual units sampled?
A. 850
B. 854
C. 867
D. 844
View Answer
Answer: Option B
Explanation:
We know,I=nARLPutting n=7 and ARL=122, we get, I = 854.
Question 15
If β- risk of any process is 0.75, what will be the ARL for that process?
A. 4
B. 1.33
C. 0.86
D. 2
View Answer
Answer: Option A
Explanation:
ARL is given by,ARL=\(\frac{1}{1-β}\) Putting β=0.75, we get ARL=4.
Question 16
In phase I application of x and R chart, the control limits obtained from the equations are treated as ____________
A. Final limits
B. Trial limits
C. Warning limits
D. Pattern limits
View Answer
Answer: Option B
Explanation:
The obtained limits from the equation of control limits for a x and R chart, are generally treated as Trial limits. They allow us to determine whether the process was in control when the m initial samples were taken.
Question 17
LCL for the R chart is given by __________
A. D3 R
B. D2 R
C. R – D3 R
D. d2 R
View Answer
Answer: Option A
Explanation:
LCL for an R chart is always given by the following equation,LCL = D3 R.
Question 18
Never attempt to interpret the x chart when the R chart indicates the out of control condition.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
It is easy to eliminate the assignable causes in the x chart by eliminating the assignable causes in the R chart. This implies, if there is indication of out-of-control condition of process from the R chart and x chart; then first, R chart must be interpreted.
Question 19
Once a set of reliable control limits is obtained, we use the control chart for monitoring future production. This is called __________
A. Phase I control chart usage
B. Phase II control chart usage
C. Phase III control chart usage
D. Phase IV control chart usage
View Answer
Answer: Option B
Explanation:
The use of reliable control limits to monitor the future production from a process, is generally mentioned as the Phase II application of control chart while, setting the trial control limits to monitor the process is called the Phase I application.
Question 20
Process capability generally uses __________
A. Specifications
B. Control Limits
C. Process standard deviation
D. Mean of any one sample
View Answer
Answer: Option B
Explanation:
Process capability studies make use of the specifications of any certain Critical-to-quality characteristic or quality characteristic to estimate the performance of any process.
Question 21
Process standard deviation is necessarily equal to the sample standard deviation of the same process.
A. TRUE
B. FALSE
View Answer
Answer: Option B
Explanation:
It is not necessary that the sample standard deviation will always be equal to the process standard deviation, for a same process. This is because; there may be assignable causes of variation while the sample is being produced by the process.
Question 22
Process variability can only be described and monitored by the s control chart.
A. TRUE
B. FALSE
View Answer
Answer: Option B
Explanation:
The process variability can be monitored with either a control chart for standard deviation, called the s control chart, or a control chart for the range, called an R control chart.
Question 23
Quantities that can be numerically measured, can be plotted on a _________ control chart.
A. X bar
B. P chart
C. C chart
D. np chart
View Answer
Answer: Option A
Explanation:
A quantity that is measured on a continuous scale, i.e. it is numerically measured, can be plotted on a control chart type named, X bar control chart.
Question 24
S chart is used to monitor _________ of a quality characteristic.
A. Mean
B. Range
C. Variability
D. Attributes
View Answer
Answer: Option C
Explanation:
S chart is a control chart used to monitor the variability of a process quality characteristic. It is variable chart as it is used for monitor variability of variables.
Question 25
Shift in process level can be seen on the control charts when __________
A. Operator fatigue occurs
B. Temperature changes
C. Over-control of process
D. New workers introduction
View Answer
Answer: Option D
Explanation:
Shift in the process level is a phenomenon seen on the control chart patterns. It occurs when there is introduction of new workers, or there is a change of methods.
Question 26
Slope of OC curve for x bar chart will _________ when sample size is increased.
A. Decrease
B. Increase
C. Remain same
D. Decrease then increase
View Answer
Answer: Option B
Explanation:
The OC curve is the curve between the β- risk against the magnitude of the shift in mean expressed in std. deviation units for different sample size. Its slope decreases as the sample size is increased.
Question 27
Specifications have the same meaning as ____________
A. Control limits
B. UCL
C. LCL
D. Tolerances
View Answer
Answer: Option D
Explanation:
The tolerance for a variable quality characteristic is generally having the same meaning as specifications of a product, i.e. the desired values for that quality characteristic.
Question 28
Stratification is defined as ________
A. Tendency for the points to cluster artificially around the center line
B. Shift in the process level
C. Continuous movement of points in one direction
D. When the points fall near or slightly outside the control limits
View Answer
Answer: Option A
Explanation:
Stratification is defined as the tendency of the points on a control chart, to cluster around the center line of the control chart. It occurs very frequently while applying control charts to a process.
Question 29
The 3 sigma limits on x bar control charts imply that the type I error probability is __________
A. 0.0012
B. 0.0072
C. 0.0027
D. 0.0037
View Answer
Answer: Option C
Explanation:
The 3 sigma control limits on x bar control charts will imply that the type I error probability is 0.0027 or 0.27%. It will give 2700 defectives per million units of production.
Question 30
The assumption that links normality to the control charts is ___________
A. The underlying distribution of the quality characteristic is normal
B. The normal mean will be equal to the process mean
C. The normal distribution is not the correct distribution for all the quality characteristic
D. Every distribution is a part of normal distribution
View Answer
Answer: Option A
Explanation:
There is an assumption that links the normality to the control charts in the development of the performance properties of x bar and R charts; that is, the underlying distribution of the quality characteristic is normal.
Question 31
The center line for a \(\bar{\bar{x}}\) chart denotes ________
A. Mean of any sample
B. Mean of means of the sample
C. Mean of any sample + 0.5
D. (Mean of any sample) / 0.5
View Answer
Answer: Option B
Explanation:
The center line for a \(\bar{\bar{x}}\) chart is generally mean of means of all the samples taken from a process. This gives more accurate results than choosing the mean of any sample to be taken as Center line.
Question 32
The control limits obtained by specifying the type I error level for the test, are called ________
A. Probability limits
B. Trial limits
C. Error limits
D. Unreliable limits
View Answer
Answer: Option A
Explanation:
It is possible to define the control limits for a control chart by specifying the type I error level. The limits obtained by this way, are called the Probability limits for the control chart.
Question 33
The lower control limit for an x bar control chart is lesser than the mean of means of the samples taken.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The lower control limit for any control chart is expressed byLCL = \(\bar{\bar{x}} – A_2 R\) So it is lower than process mean or the mean of means of samples taken.
Question 34
The natural variability of the process is measured by ____________
A. Process mean
B. Sample standard deviation
C. Process standard deviation
D. Sample mean
View Answer
Answer: Option C
Explanation:
The natural variability of any process is the main factor affecting the control limits of any quality characteristic while plotting a control chart. They are measured by process standard deviation, σ.
Question 35
The probability of not detecting “an in-control shift” of the mean of the process is said to be the _____
A. α – Risk
B. β – Risk
C. γ – Risk
D. δ – Risk
View Answer
Answer: Option B
Explanation:
If the mean of a process shifts from one value to another value with process being in-control, and shift is not detected on the control chart, the probability of this event is called the β – Risk.
Question 36
The process standard deviation is given by __________
A. R/d2
B. Rd2
C. 1/d2
D. R/d
View Answer
Answer: Option A
Explanation:
The process standard deviation may be estimated by using the following equation,\(\hat{σ} = \frac{\bar{R}}{d_2}\)
Question 37
Tolerances are said to be ________
A. limits of natural variability
B. Statistical limits of variability
C. Limits determined by the customers of the product
D. Limits of inherent process variability
View Answer
Answer: Option A
Explanation:
The natural variability varies from a certain highest value to some lowest value. These limits of natural variability are also called as Tolerance.
Question 38
Toughness of a bolt mount on a tank is __________
A. An attribute
B. A variable
C. Variable and an attribute
D. Variability
View Answer
Answer: Option B
Explanation:
A quality characteristic having a numerical measurement on a continuous scale is called a variable. As the toughness of a bolt is a continuous quality characteristic, it is called a variable.
Question 39
Unlike x chart, which measures between-sample variability only, an R chart is used to monitor ____
A. Both between-sample variability and within-sample variability
B. Within-sample variability only
C. Between-sample variability only
D. Neither between-sample variability nor within-sample variability
View Answer
Answer: Option B
Explanation:
A R chart is a chart which uses sample ranges to calculate its center line and control charts. So it only measures within-sample variability, i.e. the instantaneous variability at a given time.
Question 40
What type of chart will be used to plot the number of defectives in the output of any process?
A. x bar chart
B. R chart
C. c chart
D. p chart
View Answer
Answer: Option D
Explanation:
The number of defectives in the samples of the output of a process is monitored by the p chart and the number of defects is monitored by a “c chart”.
Question 41
When R chart is out of control, we __________
A. Eliminate the out-of-control points and recalculate the control limits
B. Take one more sample and recalculate the control limits
C. Eliminate the out-of-control points and the nearest two points, and recalculate the control limits
D. Take no action
View Answer
Answer: Option A
Explanation:
When R chart is out of control, we often eliminate the out-of-control points and recompute a revised value of R bar. This will help us recalculate the control limits.
Question 42
When the upper and lower natural tolerance limits are equal to the upper and lower specification limits, the process capability ratio, cp is ________
A. Greater than 1
B. 0
C. Less than 1
D. Equal to 1
View Answer
Answer: Option D
Explanation:
When the natural tolerance limits are having a equal value to the specification limits for a quality characteristic, the process capability ratio, cp is having a value equal to 1.
Question 43
Which chart should be interpreted first when both, x chart, and R chart are indicating a non-random behavior?
A. x chart
B. R chart
C. X and R chart
D. Trial Limits
View Answer
Answer: Option B
Explanation:
It is a property of control charts for x bar and R, that if they both indicate non-random behavior, and if R chart is interpreted first to delete the assignable causes in it, it will automatically delete assignable causes in x bar chart.
Question 44
Which of these is a cause of trend patterns on a control chart?
A. Gradual wearing out of some critical process component
B. Operator fatigue
C. Environmental changes
D. Over-control
View Answer
Answer: Option A
Explanation:
A trend or continuous movement in one direction on a control chart is generally caused by gradual wearing out of some critical process component like deterioration of a tool.
Question 45
Which of these should be plotted on the x bar chart?
A. Counts
B. Defects
C. Problems Solved
D. Measurements
View Answer
Answer: Option D
Explanation:
Counts, defects and problems solved are all quantities which increase in a discrete amount. Measurements increase in a continuous way. Only Continuous quantities are plotted on the x bar chart.
Question 46
Which term is having a closest meaning as Sampling Distributions?
A. Control charts
B. On site inspection
C. Whole lot inspection
D. Acceptance sampling
View Answer
Answer: Option A
Explanation:
The term “control charts” is having a closest meaning to “sampling distribution” because, control charts are also plotted on the data obtained from the sample inspection and also, they show variation in sample data.
Question 47
X chart is a ____________
A. Attribute control chart
B. Variable control chart
C. Neither a variable control chart nor an attribute control chart
D. Falls in the category of both variable and attribute control charts
View Answer
Answer: Option B
Explanation:
Mean is only an asset of a variable quality characteristic. As x denotes mean of a variable, x chart is counted in the variable control chart category.