ITPEC FE Subject A October 2025 Question 13
ITPEC FE Subject A October 2025 — Question 13 of 60
FCFS Scheduling — Average Turnaround Time — calculate average completion time when processes run in arrival order.
Given processes A, B, C, D, E with running times 10, 6, 2, 8, 4 ms (FCFS order):
Turnaround = cumulative completion time for each process:
- A: 10
- B: 10 + 6 = 16
- C: 16 + 2 = 18
- D: 18 + 8 = 26
- E: 26 + 4 = 30
Average = (10 + 16 + 18 + 26 + 30) / 5 = 100 / 5 = 20
Why not others:
- (a) 14 — incorrect cumulative sums
- (b) 19.2 — wrong calculation order
- (d) 22 — arithmetic error
Key rule: In FCFS, turnaround time for process i = sum of running times of all processes up to and including i. Average = sum of all turnaround times ÷ number of processes.
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