How much staff do you need?

How much staff do you need?


In this report, after I carefully analyze the situations of the garage, I recommend the mixmise number of the staff should be employed, which can basically ganratee the work to be finished everyday. The results is that the gargare should employ 2 Unskilled labour, 3 Mechanic Grade B and 6 Mechanic Grade A, which can finish the task in 95 occasions out of 100.


The problem in this case is to decide how many staffs of each kind should be emplyed to finish the tasks of the garage everyday.It is important beacause it relative to the labour cost of the garage and the effciency of the work.To slove this proble, software Simul 8 was used to simulate the case as real life and analize the results from many times runs.

The results of my finding can ganaretee 95 occasions out of 100 which can totally finish the task everyday.

Main body

Problem Findings

After analyses the cases will happen in the garage everyday,I found that if there only have 1 people of each staff, there were some cars remain in the queues for Regular service ,queue for Major service, Brake test and Valet which relusts in the unfinished tasks. So it is ovbiously that the problem is the efficiency of these services. The limited staff lead to this low efficency. Hence, the garage shoule emply more staffs to ensure the tasks can be finished. But the number of each staff should staff should be carefully examined, which related to the cost of the garage.


When cars arrival, they first enter the reception. The average time of check in is 10 mimutes,so if the following car arrival at reception within 10 mimutes it should wait for its turn. After the first car finished check in, it go to regular sevice. Mechine A staff should go to regular sevice to do the regular service. When the regular service have been finished, Staff A can be released whenever the other services need them.

The regular service , major service, brack test and clutch repair need staff mechine A, and staff A can do one thing at one time, so the garage should employ much more mechine A to allow them provide different service at the same time. Also when more mechine A do in the same service center, they can improve the efficiency thus reduce the queue of waitting.

In average, there are 59.96 cars arrival everyday, and 24 cars arrival in the garage before 12:00, all 24 cars can be almost finish. But the numbers of cars are changing day from day. After try again and again, i got an optional solution, which is 6 Mechine A, 3 Mechine B and 2 Unskilled labor. The unilities of Mechine Grade A is 72.51%, average use numer is 4.35. Mechine B's unilities is 32.47%, average 0.97 people in work.Unskilled labor's unilitis is 38.14%, average 0.76 staff busy with work.This solution can only generate 95 occasions out of 100 which cars can be finished in time at the end of the day.

Under this solution, in average, the Reception can finish 23.81 cars, Regular service center finish 23.33 cars, Brack test complete 14.15 cars, Finial check finish 14.08 jobs, Major service deal with 10.02 cars,Chulth repair tackle 3.83 cars, Gear box sevice 0.77 cars, Type repacement complete 3.01 cars, 14.59 cars can be finished in Valet center and 7.45 cars can be completed by Valet and polish. Totally 22 cars can finished in time at the end of the day.

The garage also can reduce each kind of statt but it will results in more unfinished cases. The garage also can employ more staffs to improve the efficecy,but it will cost much more. So this solution is the most suitable one.


To sum up, I recommend that the gargare should at least emply staffs with 2 Unskilled labour, 3 Mechanic Grade B and 6 Mechanic Grade A. This is a sensible policy for the garage to operate, because it can improve the efficiency of the work and ganrantee most of the days can finish the work, and it also can cut the cost of the employ and maximisi the profit of the gargare.


Technical Report -------- Modelling process

Step 1:

Draw activity diargram. Then use the SIMUL 8 to build the initial model. Set an entry point , named “Arrival”; then creat 10 work centers to present activities and Storage Area as queues, rename the work centers with “Reception” “Regular service” “Brake Test” “Final Check” “Major service” “Valet” “Clutch repair” “Tyre replacement” “Gearbox” “Valet and polish”; at last add the complete point.

Then The initial model as follow:

Step 2:

Caculate the percentage of the queues which routing out by the activities. Then set the percents of the “Routing out” of the activities. There are three work centers have not only one queue after that, so should set the percent of “Routing out”

Work center Regular Service: set “Rouint out”à “Percent” à “55% Queue for Brake Test” and “45% queue for Major Service” ,which is showed in the below diagram:

Work center Final Check, set “Routint out”à “Percent” à “10% Queue for Brake Test” and “90% queue for Valet”;

Work center Major Service, set “Routint out”à “Percent” à “20% queue for Valet” , “40% queue for Clutch repair”, “32% queue for Tyre replacement” and “8% queue for Gearbox”

Step 3:

Set the Distribution for each activity by double click each work center.




Exponential, inter-arrival time 10 min


Fixed, 10 min

Regular Service

Uniform (45,90)

Brake Test


Final Check




Major Service


Clutch repair


Tyre replacement




Valet & polish


Step 4:

Create three kinds of resoure., then Resource icon will appear:

The number 10 above the Resource indicates the number of resources available initially. Then Resources can be added to Work Centers from the list. This allow operations to take place at work centers when they are present, and stop them taking place when they are not.

Step 5:

Set the “Clock” for the whole simulation process. Set the start time to 8am (08:00), and the Time in each day to 10:00. The clock will now run for 10 hours per day starting at 8am. Next change the “Results Collection Period” to 600.

Step 6:

Creat two labels “ arrival time” and “route”.

Inorde to prevent any cars entering the garage after 12.00 I use the VB logic to the lale action at the “Arrial point”. Add lable” arrival time”, then set VB code as “If arrival time <= 240, set route=1”, which means before 12:00 the cars will enter the queue to repection; then “else set the route=2”.

Step 7:

Use the “ Dummy work center” between arrival piont and the queue to reception,

Then add one more queue routing out by the Dummy, which means the cars arrival after 12:00.

Then routing out the Dummy 2 routs

Step 8:

Besause in real life, different random numbers of car arriving every day in each individual repetition. Using the “Conduct Trial”, Simul8 do this automatically. It is a more realistic impression a number of concurrent runs.

Step 9:

After analyse the run process and the results, I find there are most cars remained in the queue for Regular service and major service and some remained in the queue for brake test ,valet. So each kinds of resouses are not enough to do the services.

Step 10:

Set all the resourse numeber to 10, then run the model again and again. Try to reduce the numbers of the three kinds of resource by ecah run, then run the model again. At last, when the number of resourses are “ Machine A” =6, “ Machine B”=3, “ Unskilled labour”=2, the results showed the tasks can be finish normally.

The final model:


The Results Summary automatically produces upper and lower 95% Confidence Intervals. This can be interpreted as on 95 occasions out of 100 a result between the upper and lower 95% range figures is predicted.

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