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Unformatted text preview: Chapter 08A - Waiting Line Analysis CHAPTER 8A WAITING LINE ANALYSIS Review and Discussion Questions 1. Cultural factors affect waiting lines. For example, fast checkout lines (e.g., 10 items of less) are uncommon in Japan. Why do you think this is so? A manager of a major store chain told one of the authors that it "didn't make sense to give preferential treatment to people who buy less from you. 2. How many waiting lines did you encounter during your last airline flight? Possibilities include: baggage check-in, ticket counter, security check, check-in at gate, at boarding, and baggage pickup. 3. Distinguish between a channel and a phase. A channel is the initial service point of a queuing system. A phase refers to the number of stages that the service points provide. It is possible to have single to multiple service channels and single to multiple service phases. 4. What it the major cost trade-off that must be made in managing waiting line situations? The classic trade-off is between the cost of waiting for service versus the cost of providing additional service capacity, e.g., the cost of idle WIP versus the cost of adding more workers and machines to process the inventory. 5. Which assumptions are necessary to employ the formulas given for Model 1? Poisson arrival rates, exponential service rates, which imply a purely random process, but with a known mean (and hence known variance). Also assumed is that the process has reached a point of stochastic equilibrium. In other words, steady state conditions prevail. 6. In what way might the first-come, first served rule be unfair to the customer waiting for service in a bank or hospital? In a bank, FCFS may be perceived to be unfair by customers who have large accounts, but who must wait while the less "important customers obtain service. In a hospital, especially in an emergency room, FCFS is probably the exception rather than the rule. FCFS would be unfair when a patient with a minor problem is treated before another experiencing severe pain. 7. Define, in a practical sense, what is meant by an exponential service time. An exponential service time means that most of the time, the service requirements are of short time duration, but there are occasional long ones. Exponential distribution also means that the probability that a service will be completed in the next instant of time is not 118 Chapter 08A - Waiting Line Analysis dependent on the time at which it entered the system. We can see that a barber, for example, does not fit an exponential distribution in either case. The barber has an average time for cutting hair, and a person who has been sitting in the chair getting a haircut for the past 15 minutes has a higher probability of being completed in the next minute than a person who just walked in and sat down....
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- Spring '11