From my understanding since FCFS is non-preemptive, the time until it is selected by the scheduler for the first time is the same as the total time spent in the ready queue, thus the response time is always the same as the waiting time. But my professor says in some cases it isn’t true.

I tried asking chatGPT as well but it says that “In a First-Come, First-Served (FCFS) scheduling algorithm, the response time and waiting time are indeed often the same, but not always”. And if I ask for examples it starts saying some nonsense like

“P3 starts execution after P2 finishes at time 8 and completes at time 12. Its waiting time is 4 units (time between arrival and start of execution), and its response time is also 4 units.
As we can see, for P1, its waiting time and response time are indeed the same since it’s the first process. However, for P2 and P3, their waiting time includes the time they wait for previous processes to complete their execution, making their waiting time longer than their response time.”