1. FCFS Scheduling:

For instance:

Process                                         Burst Time

P1                                                   24

P2                                                   3

P3                                                   3

P4                                                   15

Suppose the arrived order is P1,P2,P3,P4

So the average waiting time is (24+27+30)/4 = 20.25

2. SJF Scheduling

For instance:

Process                       Arrived Time                       Burst Time

P1                                 0                                            7

P2                                 2                                            4

P3                                 4                                            1

P4                                 5                                            4

So the average waiting time is ((7-4) + (8-2) + (12-5))/4 = 4

3. RR Scheduling

For instance:

Process                                         Burst Time

P1                                                   94

P2                                                   34

P3                                                   69

P4                                                   77

Suppose time block is 20

The order is  P1，P2，P3，P4，P1，P2，P3，P4，P1，P3，P4，P1，P3,P4，P1