 Solution

The preemptive policy improves B's scheduling turnaround time from 17 to 10 ms and the mean from 16.5 to 14 ms. A finishes later, at 18 rather than 16 ms, and the total completion time rises from 17 to 18 ms. Thus preemption improves mean turnaround here; nonpreemption gives the shorter makespan here.

The result illustrates different scheduling objectives, not a universal winner. These calculations assume negligible context switch overhead; charging for the additional switches could change the comparison. Both policies perform the same 15 ms of useful CPU work.