# Operations Management - Queue calculations

Hi there:

I'd like some help with these 3 queuing problems. Examples and explanations are given. Thanks!

Queue Management

There is the "Queue calculations.xls" spreadsheet for this assignment. Included is an 'instructions' document with helpful information.

Before attempting this assignment, anyone can review the example problems and solutions, which will get someone familiar with the solution approaches. **Note that the last question in this set has to do with finite waiting space. It is not needed for this assignment but is included in case you are interested.

Please see ** ATTACHED ** file(s) for complete details!!

#### Solution Preview

** Please see the attached Word & Excel files. **

Thanks

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1. The check-in line at Alpha Airlines has two agents who serve all passengers during peak hours. Arrivals to the check-in counter are Poisson with a mean of 50 passengers per hour. Approximately, thirty percent of the arrivals are Priority Class (e.g., First Class, Gold members, etc) while the remainder holds coach tickets. The time that a passenger spends at the ticket check-in counter with an agent is exponentially distributed with a mean of 1.44 minutes. Alpha promises that if a passenger waits in line for more than 5 minutes, a coach passenger will be awarded 500 frequent flyer miles while a Priority Class passenger will be awarded 1000 miles. Currently, all passengers go through the same queue for check-in.

a) How many total miles are awarded per hour on average currently?

This is M/M/m with l = 50/hour and 1/m = 1.44 minutes= 1.44/60 hours. Therefore, we use the "MMm" spreadsheet and set cells E2-D4 are 50, 41.667 and 2.

From spreadsheet, we get

Utilization =60.00%

p0 =Probability that the system is empty=0.25

Lq = Expected queue length =0.675

Ls = Expected number in system =1.875

Wq = Expected time in queue =0.0135 hours

Ws = Expected total time in system =0.0375 hours

Now we calculate the probability of waiting in queue for more than 5 minutes i.e. 5/60 hours. Change the value in cell E22 to =0.0833 hour

Prob(waiting in queue > t) = Prob(wait) * e-(mm-l)t

P(Wait>5 minutes) = 0.02798

Since 30% of arrivals are priority, the total miles awarded per hour on average is

=30%*50*0.02798*1000+70%*50*0.02798*500

=909.33 miles

b) Management is considering the creation of two separate lines, one for each of the two classes of passengers. In this situation, each check-in line will have one agent who will serve their respective passengers; line switching will not be allowed. Find the average total miles awarded hourly under this configuration.

Here, we will have two separate systems for the two types of customers.

For priority customers:

The system is M/M/1 with l = 15/hour and 1/m = 1.44 minutes= 1.44/60 hours. Therefore, we use the "MMm" spreadsheet and set cells E2-D4 are 50, 41.667 and 1.

From spreadsheet, we get

Utilization =36.00%

p0 =Probability that the system is empty=0.64

Lq = Expected queue length =0.2025

Ls = Expected number in system =0.5625

Wq = Expected time in queue =0.0135 hours

Ws = Expected total time in system =0.0375 hours

Now we calculate the probability of waiting in queue for more than 5 minutes i.e. 5/60 hours. Change the value in cell E22 to =0.0833 hour

Prob(waiting in queue > t) = Prob(wait) * e-(mm-l)t

P(Wait>5 minutes) = 0.03901

Total miles ...

#### Solution Summary

The expert provides queue calculation for operations management spreadsheets.