1.Process makes the operating system can do different things in the same time and they would not influent each other.
2.
a)
FCFS:
P1 P2 P3 P4 P5
0 10 11 13 14 19
SJF:
P2 P4 P3 P5 P1
0 1 2 4 9 19
Non-preemptive:
P2 P5 P1 P3 P4
0 1 6 16 18 19
RR:

P1 P2 P3 P4 P5 P1 P3 P5 P1 P5 P1 P5 P1 P5 P1 P1 P1 P1 P1
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

b)
FCFS:
P1:10(ms) p2:11(ms) p3:13(ms) p4:14(ms) p5:19(ms)
SJF:
P1:19(ms) P2:1(ms) P3:4(ms) P4:2(ms) P5:6(ms)
Non-preemptive