OPS 574 Wk 3 - Practice: Formative Assessment

If capacity exceeds demand, then all flow units are served.

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The denial of service probability decreases if more servers are added and nothing else changes.

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Conceptual Question 17-8 Which of the following…

Which of the following most directly expresses the motivation behind the expression “buffer or suffer”?

multiple choice

• Adding inventory to a process is likely to increase the flow time.
• To increase capacity, it is important to pool queues.
• If you want to increase the capacity of a process, add capacity first to the bottleneck.
• If there is variability in the arrival process or in processing times, make sure there is sufficient inventory between stages; otherwise, capacity will be reduced.
• Variability in the service process reduces capacity more than variability in the arrival process.

Conceptual Question 17-7 In the Erlang loss model…

In the Erlang loss model, pooling is an effective strategy because it always increases implied utilization.

Conceptual Question 17-9 At the Millbrook High…

At the Millbrook High School cafeteria, students proceed along a series of stations in a single line: (1) get tray and utensils, (2) choose food, (3) select beverage, (4) pay. The school is concerned that students are taking too long to get their meal. The school has analyzed the capacities of each of the four steps in isolation and found there exists sufficient capacity at each resource in isolation. Which of the following is most likely to be causing the congestion?

multiple choice

• The bottleneck is probably at the last station because capacity is reduced the most when the bottleneck is at the end of the process.
• The implied utilization of the bottleneck is too low.
• Due to variability in processing times, both blocking and starving could be occurring.
• The process must be demand-constrained.
• The stations have similar utilizations.

Conceptual Question 17-4 In the Erlang loss model…

In the Erlang loss model, which best describes the relationship between implied utilization and utilization?

multiple choice

• Implied utilization is always greater than utilization.
• Implied utilization is only greater than utilization when implied utilization is greater than 100 percent.
• Implied utilization, like utilization, does not exceed 100 percent.
• Implied utilization is the same as utilization.

Conceptual Question 17-3 In the Erlang loss model…

In the Erlang loss model, which of the following most likely increases lost demand?

multiple choice

• An increase in the average interarrival time
• An increase in the average processing time
• An increase in the number of servers
• A decrease in implied utilization

Conceptual Question 17-5 In the Erlang loss model…

In the Erlang loss model, which of the following is a benefit of reducing the variability of processing times?

multiple choice

• The denial of service probability decreases.
• The flow rate increases.
• Implied utilization increases.
• Utilization increases.
• All of the choices are .
• None of the choices are .

Conceptual Question 17-6 In the Erlang loss model…

In the Erlang loss model, system A has 5 servers and an implied utilization of 125 percent, while system B has 15 servers and an implied utilization of 125 percent. Which of the following statements is true?

multiple choice

• System A has the higher utilization because it has fewer servers relative to the potential demand.
• The two systems have the same utilization because they have the same implied utilization.
• System B has a higher utilization because the fraction of lost demand is lower in that system.
• More information is needed to determine which system has the higher utilization.