Solution

The correct answer is 4.66.

Key Points

•  From the given chart, let's prepare the Gantt chart.
  
• From the above Gantt Chart, let's prepare the Turn Around Time i.e., Completion Time - Arrival Time.
  • Turn-around time of P1 is = 12-0= 12.
  • Turn-around time of P2 is = 5-1= 4.
  • Turn-around time of P3 is = 21-2= 19.
• Let's calculate the waiting time for each process i.e., Waiting Time = Turn Around time - Burst Time.
  • Waiting time of P1 is = 12-8= 4.
  • Waiting time of P2 is = 4-4= 0.
  • Waiting time of P3 is = 19-9= 10.
• So the average waiting time is = (4+0+10)/3 = 4.66.

Thus the correct answer is 4.66.

Additional Information

• Turn Around Time(TAT): The Turn Around Time can be estimated by calculating the difference between the arrival time and the submitting time in the process. 
• Waiting Time(WT): When a process is in a ready state and waiting for accessing the CPU, then the process is in a waiting state.
• Burst Time: When the CPU needs some time for executing a process, then it is known as burst time.