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532 CHAPTER 12 SIMULATION

Typically, three employees operate each store Service Time (minutes) Probability
during peak periods; two clerks take and fill orders,
1 0.20
and a third clerk serves as cashier and store super-
2 0.35
visor. Effortless Events is considering a revised store
3 0.30
design in which computerized order-taking and pay-
4 0.10
ment are integrated with specialized warehousing
5 0.05
equipment. Management hopes that the new design
Total 1.00
will permit operating each store with one clerk. To
determine whether the new design is beneficial,
Effortless Events’s management would like you
management decided to build a new store using
to develop a spreadsheet simulation model of the
the revised design.
new system and use it to compare the operation
Effortless Events’ new store will be located near
of the system using the following three designs:
a major shopping centre. Based on experience at
other locations, management believes that during
Design
the peak late afternoon and evening hours, the time
between arrivals follows an exponential probability A One channel, one clerk
distribution with a mean of six minutes. These peak B One channel, two clerks
hours are the most critical time period for the com- C Two channels, each with one clerk
pany; most of their profit is generated during these
peak hours. Management is especially concerned with how
An extensive study of times required to fill orders long customers have to wait for service. Research
with a single clerk led to the following probability has shown that 30 per cent of the customers will wait
distribution of service times. no longer than six minutes and that 90 per cent will
wait no longer than ten minutes. As a guideline,
management requires the average waiting time to
Service Time (minutes) Probability
be less than 1.5 minutes.
2 0.24
3 0.20 Managerial Report
4 0.15
Prepare a report that discusses the general develop-
5 0.14
ment of the spreadsheet simulation model, and
6 0.12
make any recommendations that you have regard-
7 0.08
ing the best store design and staffing plan for Effort-
8 0.05
less Events. One additional consideration is that the
9 0.02
design allowing for a two-channel system will cost an
Total 1.00
additional E10 000 to build.
In case customer waiting times prove too long 1 List the information the spreadsheet simulation
with just a single clerk, Effortless Events’s manage- model should generate so that a decision can be
ment is considering two alternatives: add a second made on the store design and the desired
clerk to help with bagging, taking orders and related number of clerks.
tasks, or enlarge the drive-thru area so that two 2 Run the simulation for 1000 customers for each
cars can be served at once (a two-channel system). alternative considered. You may want to consider
With either of these options, two clerks will be making more than one run with each alternative.
needed. With the two-channel option, service times [Note: Values from an exponential probability
are expected to be the same for each channel. With distribution with mean can be generated in Excel
the second clerk helping with a single channel, serv- using the following function: ¼ *LN(RAND()).]
ice times will be reduced. The following probability
3 Be sure to note the number of customers Effortless
distribution describes service times given that
Events is likely to lose due to long customer waiting
option.
timeswitheachdesignalternative.

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