1.FCFS Scheduling:  process:p1,p2,p3.  burst time:23,5,5. The average waiting time is (23+5+5)/3=11.

2.SJF Scheduling:  process:p1,p2,p3,p4.  burst time:12,5,7,6. The average waiting time is (18+0+11+3)/4=8.

3.priority scheduling:  process:p1,p2,p3,p4.  burst time:8,12,4,6.   priority:3,2,4,1.  The average waiting time is (18+6+26+0)/4=12.5.

4.RR Scheduling:process:p1,p2,p3.  burst time:23,5,5. If we use a time quantum of 6 milliseconds, the average waiting time is (10+6+11)/3=9.

5.multilevel queue scheduling。