ITPEC FE Morning October 2018 Question 17
ITPEC FE Morning October 2018 — Question 17 of 80
FCFS Average Turnaround Time — calculate mean completion time for sequentially executed processes.
All processes arrive at t = 0, executed in order P1 → P2 → P3 → P4 → P5.
Completion times (cumulative burst):
- P1: 14
- P2: 14 + 5 = 19
- P3: 19 + 6 = 25
- P4: 25 + 5 = 30
- P5: 30 + 7 = 37
Turnaround time = completion time − arrival time. Since all arrive at 0, turnaround = completion time.
Average = (14 + 19 + 25 + 30 + 37) / 5 = 125 / 5 = 25
Why not others:
- (a) 10 — no valid interpretation produces this value
- (b) 15 — no valid interpretation produces this value
- (c) 20 — a common trap if waiting time is confused with turnaround time
Key rule: In FCFS with all arrivals at t = 0, turnaround time for process i equals the cumulative sum of burst times from process 1 through i.
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