7. Consider a bank where potential customers arrive atrate of 60 customers per hour. However, because oflimited space, one out of every four arriving customersfinds the bank full and leaves immediately (withoutentering the bank). Suppose that the average numberof customers waiting in line in the bank is 3.5. Howlong will a typical entering customer have to wait inline? (Hint: In Little’s formula, l refers only to customers who enter the system.)

7. Consider a bank where potential customers arrive atrate of 60 customers per hour. However, because oflimited space, one out of every four arriving customersfinds the bank full and leaves immediately (withoutentering the bank). Suppose that the average numberof customers waiting in line in the bank is 3.5. Howlong will a typical entering customer have to wait inline? (Hint: In Little’s formula, l refers only to customers who enter the system.)

Practical Management Science

6th Edition

ISBN:9781337406659

Author:WINSTON, Wayne L.

Publisher:WINSTON, Wayne L.

Chapter12: Queueing Models

Section12.5: Analytic Steady-state Queueing Models

Problem 9P

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Consider an M/G/1/GD/∞/∞ queuing system in which anaverage of 10 arrivals occur each hour. Suppose that eachcustomer’s service time follows an Erlang distribution, withrate parameter 1 customer per minute and shape parameter 4.a Find the expected number of customers waiting inline.b Find the expected time that a customer will spend inthe system.c What fraction of the time will the server be idle?
Consider a bank where potential customers arrive at rate of 60 customers per hour. However, because of limited space, one out of every four arriving customers finds the bank full and leaves immediately (without enteringthe bank). Suppose that the average number of customers waiting in line in the bank is 3.5. How long will a typical entering customer have to wait in line? (Hint: In Little’s formula, l refers only to customers who enter the system.)
10. Two operators handle adjustments for a group of 10 machines. Adjustment time is exponentiallydistributed and has a mean of 14 minutes per machine. The machines operate for an average of86 minutes between adjustments. While running, each machine can turn out 50 pieces per hour.Find the following:a. The probability that a machine will have to wait for an adjustmentb. The average number of machines waiting for adjustmentc. The average number of machines being servicedd. The expected hourly output of each machine, taking adjustments into accounte. Machine downtime represents a cost of $70 per hour; operator cost (including salary andfringe benefits) is $15 per hour. What is the optimum number of operators?
The cashier line of a canteen can facilitate up to 60 customers an hour. Frequenters of the canteen arrive at an average of 50 an hour. Suppose that management wants to evaluate the desirability of opening a second order-processing station so that two customers can be served simultaneously. Assume a single waiting line with the first customer in line moving to the first available server. a. How long in minutes would it take the customer from lining up until he leaves the waiting line? b.How long in minutes would a customer wait to be served on average? c.Find the probability that there are 7 customers in the system.
Suppose a supermarket uses a system in which allcustomers wait in a single line for the first available cashier.Assume that the service time for a customer who purchasesk items is exponentially distributed, with mean k seconds.Also, a customer who purchases k items feels that the costof waiting in line for 1 minute is $k1. If customers can beassigned priorities, what priority assignment will minimizethe expected waiting cost incurred by the supermarket’scustomers? Why would a customer’s waiting cost per minutebe a decreasing function of k?
Consider this situation: A manager is contemplating making changes to a single-server system that is expected to double the service rate, and still have just one server. (a). Would you (intuitively) think that doubling the service rate of a single-server system would cut the average waiting time in line in half? (b). For the sake of analysis, suppose the current system has an arrival rate of 8 customers per hour and a service rate of 10 customers per hour. If the service rate is doubled, what impact will that have on the average number waiting in line? (c). What are some managerial implications of your analysis?
20. A small bank is trying to determine the number of tellersto employ. The total cost of employing a teller is $100per day, and a teller can serve an average of 160 customers per day. On average, 210 customers arrive per day atthe bank, and both service times and interarrival times areexponentially distributed. If the delay cost per customerday is $200, how many tellers should the bank hire?
The manager of a large group of employees must decidewhether she needs another photocopying machine. Thecost of a machine is $40 per eight-hour day regardlessof whether the machine is in use. On average, fourpeople need to use the copying machine per hour. Eachperson uses the copier for an average of 10 minutes.Interarrival times and copying times are exponentiallydistributed. Employees are paid $8 per hour, and weassume that a waiting cost is incurred when a worker iswaiting in line or is using the copying machine. Howmany copying machines should be rented?
Consider an M/M/1 queue in which customers arrive at a rate of 20 per hour, and the average service time is 150 seconds. What is the average number of customers in the system, and how long, on average, does each spend in the system and in line? Answer the question also if the arrival rate increases by 10%.
The manager of a large group of employees must decideif she needs another photocopying machine. The cost of amachine is $40 per 8-hour day whether or not the machineis in use. An average of 4 people per hour need to use thecopying machine. Each person uses the copier for an averageof 10 minutes. Interarrival times and copying times areexponentially distributed. Employees are paid $8 per hour,and we assume that a waiting cost is incurred when a workeris waiting in line or is using the copying machine. Howmany copying machines should be rented?