The BCOT Widget shop overhauls and repairs all types of widgets. The shop consists of five work
stations, and the flow of jobs through the shop is as depicted below.
60% 40% A B C
D
E
90% 10%
100% (2nd time)
Regular jobs arrive at station A according to a Uniform [2,28] min inter-arrival time distribution. Rush
jobs arrive according to a Uniform [1,7] hour interarrival time distribution, and are given a higher
priority except at station C, where they are put on a conveyor and sent through a cleaning and
degreasing operations along with all other jobs. For jobs the first time through a station, processing
times are as follows.
Station Number of Machines /
Workers
Processing Time (min) Description
A 1 Uniform [10,14] Receiving clerk
B 3 Uniform [20,60] Disassembly and parts replacement
C 1 20 Degreaser
D 4 Uniform [10,90] Reassembly and adjustments
E 3 Uniform [35,45] Packing and shipping

The times listed above hold for all jobs that follow one of the two sequences 𝐴 → 𝐵 → 𝐶 → 𝐷 → 𝐸
or 𝐴 → 𝐵 → 𝐷 → 𝐸. However, about 10% of the jobs coming out of station D are sent back to B for
further work (which takes Uniform [20,40] min), and then sent to D and finally to E.
Station C breaks down at random times. The data shows that time between breakdowns follows an
Exponential distribution with mean 120 min. The repair process takes Uniform [9,11] min. When
breakdown occurs, the processing of the job in process (if any) is delayed until the repair is
completed. Simulate the system above in Simul8 and answer the following questions based on 1000
independent replications of the model, where each replication includes an 8-hour simulation
preceded by a 2-hour warm-up period. The main performance metric of interest is the mean
response time per job, overall and separately for regular and rush jobs, where a response time is the
total time a job spends in the shop.

1. Report the results for the current state of the shop. Make sure you include confidence
   intervals along with their interpretation.
2. What would happen if rush jobs did not have any priority over regular jobs? Explain your
   response.
3. The management is considering putting one additional worker at the busiest station (A, B, D,
   or E). Would this significantly improve the response time? Explain.
4. As an alternative to Q3, management is considering replacing Machine C with a faster one
   that processes a widget in only 14 min. Would this significantly improve response time?