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MSCI223 Business management
发布时间：2024-05-28
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Practice test questions
Q1. Discrete event simulation is dynamic with the time in the simulation model changing as the simulation runs. The time in the model is shown by the simulation clock. What is the duration of an event in simulation clock time?
A: Always 0
B: Always > 0 (i.e., always greater than 0)
C: 0 for conditional events and > 0 for bound events
D: > 0 for conditional events and 0 for bound events
E: Sometimes 0 and sometimes > 0 for both bound and conditional events
Q2. Consider the following statements about passive states:
I. Passive states are represented by rectangles in an activity cycle diagram.
II. The event to end a passive state is always a bound event.
III. An entity can sometimes spend 0 time (in simulation clock time) in a passive state.
Which of the above statements are true?
A: I and II only
B: II and III only
C: III only
D: I, II, and III
E: None of the other answers (i.e., a different combination of I, II and III is true)
Q3. A congruential random number generator produces a sequence of integers Ij using the equation: Ij = (a Ij-1 + c) mod m
where a, c and m are constants.
The congruential random number generator is used to generate random numbers between 0 and 1 by dividing the integers by m.
Consider the following statements:
I. If the constants are chosen well then the generator will generate every possible number between 0 and 1.
II. It is important that the constant a is a very large number (such as 231-1).
III. It is important that the constant m is a very large number (such as 231-1).
Which of the above statements are true?
A: I only
B: I and II only
C: I and III only
D: III only
E: None of the other answers (i.e., a different combination of I, II and III is true)
Q4. Consider the following statements about the event list in the 3 phase simulation process:
I. The event list only looks one step ahead for each entity.
II. The event list contains bound and conditional events.
III. The event list can never contain two events that happen at the same simulation clock time.
Which of these statements are true?
A: I only
B: I and II only
C: II and III only
D: I, II, and III
E: None of the other answers (i.e., a different combination of I, II and III is true)
Q5 – Q7. A small supermarket has 2 self-service checkout machines that customers use to pay for their shopping items. The inter-arrival time for the customers arriving at the checkouts follows the negative exponential distribution with a mean of 2 minutes. The customers form a single queue, and the customer at the front of the queue always uses the next checkout machine to become free. The times for using the checkout machines follow the uniform distribution between 1 and 7 minutes.
Simulate the supermarket using the three phase simulation method as explained in the module. For random sampling use the equations:
Negative exponential distribution with mean m: x = -m ln(1-R)
Uniform distribution between a and b: x = a + (b - a)R
where R is a random number between 0 and 1
As in the examples covered in the module, work to 2 decimal places of minutes (i.e., round each event time to 2 decimal places).
Start the simulation at time 0.00. At that time customer 1 is using checkout machine 1 and will finish at time 2.32 minutes. Customer 2 is using checkout machine 2 and will finish at time 1.77 minutes. There is 1 customer in the queue (customer 3). The next customer to arrive (customer 4) will arrive at time 2.05 minutes.
In your simulation, use these random numbers for R:
1. 0.1790
2. 0.7054
3. 0.0439
4. 0.6520
5. 0.0636
6. 0.4815
7. 0.6766
8. 0.2562
9. 0.0992
10. 0.7129
11. 0.4172
12. 0.5575
13. 0.3363
14. 0.4262
15. 0.0673
16. 0.5184
17. 0.0933
18. 0.0255
19. 0.6472
20. 0.3589
From your simulation, answer the following questions:
Q5. The time of the finish serve event (i.e., finish using the checkout machine) of customer 3 is:
A: 2.07 minutes
B: 2.16 minutes
C: 3.84 minutes
D: 7.00 minutes
E: None of the other answers
Q6. The arrival time of customer 5 is:
A: 2.14 minutes
B: 2.44 minutes
C: 3.21 minutes
D: 4.18 minutes
E: None of the other answers
Q7. The time of the finish serve event (i.e., finish using the checkout machine) of customer 5 is:
A: 5.23 minutes
B: 5.87 minutes
C: 6.60 minutes
D: 9.40 minutes
E: None of the other answers
Q8 – Q9. A small production line has three machines: M1, M2, M3. Each machine processes one part at a time. The input to Machine M1 is raw material which is always available. This means that when a part leaves M1, M1 immediately starts making the next part. Machine M1 sends the part it produces to buffer B1. Machine M2 takes a part from B1, processes it, then sends the part to buffer B2. Machine M3 takes a part from B2, processes it, then ships the part (i.e., it leaves the model). The machines are operated by hand and so the cycle time to process a part has variability. The cycle times for each machine follow a uniform distribution. The cycle times for M1 vary between 4 and 6 minutes. The cycle times for M2 vary between 3 and 7 minutes. The cycle times for M3 vary between 4.5 and 5.5 minutes
Simulate the production line using the three phase simulation method as explained in the module. For random sampling use the equations:
Negative exponential distribution with mean m: x = -m ln(1-R)
Uniform distribution between a and b: x = a + (b - a)R
where R is a random number between 0 and 1
As in the examples covered in the module, work to 2 decimal places of minutes (i.e., round each event time to 2 decimal places).
Start the simulation at time 0.00. At that time part P1 is being processed by machine M3 and will finish at time 3.70 minutes. Buffer B2 is empty. Part P2 is being processed by machine M2 and will finish at time 2.35 minutes. Buffer B1 contains Part P3. Part P4 is being processed by machine M1 and will finish at time 2.15. If more than one machine starts processing a part at the same time assume that in the three phase method the start processing events happen in the order M3, M2, M1.
In your simulation, use these random numbers for R:
1. 0.2035
2. 0.5541
3. 0.3420
4. 0.9686
5. 0.5569
6. 0.4142
7. 0.4154
8. 0.5217
9. 0.5595
10. 0.1249
11. 0.1668
12. 0.0481
13. 0.0326
14. 0.8836
15. 0.8177
16. 0.1619
17. 0.0650
18. 0.9381
19. 0.3091
20. 0.4008
From your simulation, answer the following questions:
Q8. The time that Part P3 finishes being processed by machine M2 is:
A: 5.11 minutes
B: 6.16 minutes
C: 7.57 minutes
D: 8.34 minutes
E: None of the other answers
Q9. The time that Part P2 finishes being processed by machine M3 is:
A: 6.56 minutes
B: 7.89 minutes
C: 8.54 minutes
D: 8.75 minutes
E: None of the other answers
Q10. In the conceptual modelling lecture it was stated that assumptions should be assessed for confidence and impact. For a particular assumption, confidence is the level of certainty that the assumption about the way the real system will operate is correct. Impact is the estimated effect on the model results if the assumption is incorrect. Which type of assumptions would give the most concern when assessing the conceptual model?
A: Low confidence, low impact
B: Low confidence, high impact
C: High confidence, low impact
D: High confidence, high impact
E: All assumptions are of equal concern
Q11. Service times often have durations that follow a lognormal distribution. If a random variable X is lognormal this means that LN(X) follows a normal distribution. What do the parameters of the lognormal distribution in Witness represent?
A: Mean and standard deviation of X (actual data)
B: Mean and variance of X (actual data)
C: Mean and standard deviation of LN(X)
D: Mean and variance of LN(X)
E: None of the other answers
Q12. A simulation model is being built of a warehouse. Lorries delivering goods are scheduled to arrive at 60 minute intervals. Therefore, on average the time between arrivals is 60 minutes. However, lorries may be early or late depending on traffic and other factors. On average, 75% of lorries arrive within 10 minutes of their scheduled arrival time. 20% of lorries arrive between 10 minutes and 30 minutes late. 5% of lorries arrive between 10 minutes and 30 minutes early. Should the negative exponential distribution with a mean of 60 minutes be used to model the inter-arrival time for lorries in this situation? Select the answer below that gives both the correct answer and the correct reason:
A: Yes, it should be used because this is a Poisson process with random arrivals at a constant rate
B: Yes, it should be used because the negative exponential is suitable for all arrivals processes
C: Yes, it should be used because there is some randomness in the arrivals process
D: No, it should not be used because the probability of an arrival in each instant is not constant
E: No, it should not be used because lorries arrive at exactly equal intervals
Q13. Consider the following statement about the Witness Experimenter configure options:
I. The random number skip field sets how many additional random numbers are missed out for each replication.
II. The number of replications sets the number of times each scenario is run with different random numbers.
III. The run length sets the simulation run time after the warm-up period.
Which of these statements are correct?
A: I only
B: I and II only
C: II and III only
D: I, II, and III
E: None of the other answers (i.e., a different combination of I, II and III is true)
Q14. A simulation model should have good graphics that make it easier to see what is happening in the model and how it relates to the real system. For example, using different colours or icons for different types of parts, or making the background look like the real system (e.g., the Jetty model or the triathlon model). Consider the following statements suggesting common advantages of good graphics:
I. Good graphics help with model verification.
II. Good graphics help with communication with the client.
III. Good graphics make the output statistics more accurate.
Which of these statements are correct?
A: I only
B: I and II only
C: II and III only
D: I, II, and III
E: None of A, B. C, D (i.e., a different combination of I, II and III is true)
Q15. One of the designer elements provided in Witness is a “Shift”. What is this used for?
A: Advancing the simulation clock forward
B: Setting a schedule of working and rest times
C: Setting the length of the warm-up period
D: Moving an entity from one place to another
E: Changing the value of a variable
Q16. The Witness Workbook 2 workshop on “multi-cycle machine and labor modelling” included the Witness feature of “labor pre-emption”. What does this feature do?
A: Sets a rest time for labor after completing a task
B: Moves labor to a higher priority activity that requires labor once it completes the current activity
C: Immediately moves labor to a higher priority activity that requires labor even if labor has not completed the current task
D: Provides an unlimited amount of labor in the model so that labor is no longer a constraint
E: Reduces the time for labor to complete the current activity
