Process one through three have burst times of twenty thirtyf

Process one through three have burst times of twenty, thirty-five and ten milliseconds respectively. Assume that the processes arrive at time zero and in the order: one followed by two followed by three.

What is the average waiting time using the FCFS scheduling algorithm

13.3ms

25ms

35ms

18.3ms

Solution

Since first arrived first so its waiting time is Zero. Now the second will wait till first finishes so its waiting time is 20ms. Third will wait till second is also over so its waiting time is 20ms(of 1st) + 35 ms (of 2nd) i.e. 55ms.

Average waiting time: (0+20+55)/3 = 75/3 =25ms.