title: Waiting time in FCFS is negative, why?
body: <p>Waiting time can never negative, but when I calculate the waiting time of FCFS, it is negative. What is the actual problem?</p>
  
  <p><a href="https://i.stack.imgur.com/K3lq1.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/K3lq1.jpg" alt="enter image description here"></a></p>