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518 CHAPTER 12 SIMULATION

Customer 8
l An interarrival time of 0.3 minute is generated, and customer 8 arrives
11.0 þ 0.3 ¼ 11.3 minutes into the simulation.
l From the previous row, we see that ATM 1 will be the first available. So
customer 8 starts service on ATM 1 at 12.0 minutes resulting in a waiting time
of 12.0 11.3 ¼ 0.7 minute.
l A service time of 2.2 minutes is generated resulting in a completion time of
12.0 þ 2.2 ¼ 14.2 minutes and a system time of 0.7 þ 2.2 ¼ 2.9 minutes.
l The time available for ATM 1 is updated to 14.2 minutes, and the time
available for ATM 2 remains at 12.0 minutes.
Worksheets for the one-
ATM and two-ATM From the totals in Table 12.11, we see that the average waiting time for these ten
systems are available on
the online platform that customers is only 1.0/10 ¼ 0.1 minute. Of course, a much longer simulation will be
accompanies this text. necessary before any conclusions can be drawn.

Simulation Results with Two ATMs
The Excel worksheet that we used to conduct a simulation for 1000 customers using
two ATMs is shown in Figure 12.13. Results for the first 100 customers were
discarded to account for the start-up period. With two ATMs, the number of
customers who had to wait was reduced from 549 to 78. This reduction provides a
78/900 ¼ 0.0867 probability that a customer will have to wait for service when two

Figure 12.13 Excel Worksheet for the Hong Kong Savings Bank with Two ATMs

EXCEL file

HKSB2

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