Consider the following set of processes, with the length of CPU-burst times given in milliseconds: [table]
Process | Burst Time A | 5
B | 9 C | 10 D | 6
E | 5
[/table] The processes have arrived in the order A, B, C, D and E at a time 0. a) Draw a Gantt chart illustrating the execution of the processes using FCFS.b) Calculate the overall average wait time and turnaround time for the algorithm for FCFS.The Average Wait Time is: Blank 1 Question 15[select: , 34.2, 10.3, 25.2, 30.6, 23.1, 20.1, 16.6, 14.6, 21.6] and Turnaround Time is: Blank 2 Question 15[select: , 34.2, 10.3, 25.2, 30.6, 23.1, 20.1, 16.6, 14.6, 21.6] .

Question

BlackTom AI · Accepted Answer

FCFS schedules processes in arrival order, so the Gantt chart is: A (0–5), B (5–14), C (14–24), D (24–30), E (30–35).

1) Relevant knowledge points and concepts
- FCFS (First-Come, First-Served) runs processes in arrival order without preemption.
- Turnaround time = completion time − arrival time.
- Waiting time = turnaround time − service (CPU burst) time.
- For all processes here arrival time = 0, so turnaround = completion time.

2) Step-by-step reasoning and Gantt chart
- Order given: A, B, C, D, E, all arriving at time 0.
- Execute A for 5 ms: A starts 0, finishes 5.
- Execute B for 9 ms: B starts 5, finishes 14.
- Execute C for 10 ms: C starts 14, finishes 24.
- Execute D for 6 ms: D starts 24, finishes 30.
- Execute E for 5 ms: E starts 30, finishes 35.
Gantt (time markers): 0 |A|5 |B|14 |C|24 |D|30 |E|35.

3) Calculations with intermediate steps
- Turnaround times (completion − arrival=completion since arrival=0):
  A = 5, B = 14, C = 24, D = 30, E = 35.
  Sum = 5 + 14 + 24 + 30 + 35 = 108.
  Average turnaround = 108 / 5 = 21.6 ms.
- Waiting times (turnaround − burst):
  A = 5−5 = 0,
  B = 14−9 = 5,
  C = 24−10 = 14,
  D = 30−6 = 24,
  E = 35−5 = 30.
  Sum = 0 + 5 + 14 + 24 + 30 = 73.
  Average waiting = 73 / 5 = 14.6 ms.

4) Why the correct answer is correct
Because FCFS yields the computed completion times above, the turnaround and waiting values follow directly from the definitions; arithmetic gives 21.6 and 14.6 respectively.

5) Why other options are incorrect
Other numeric choices (e.g., 34.2, 10.3, 25.2, etc.) do not match the sums/divisions shown above; they would correspond to different schedules or incorrect arithmetic. The calculated averages 14.6 (waiting) and 21.6 (turnaround) are the only values consistent with the FCFS order and given burst times.

6) Conclusion
Average wait time = 14.6 ms and average turnaround time = 21.6 ms, which matches the provided answers.

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