What shall be the average waiting time per process if we know that 10 processes (on average) arrive every second and there are normally 20 processes in the queue?

Using Little’s Law → $N = \lambda \times W$ where

$N = 20$ (average number of processes in the system)

$\lambda = 10$ (arrival rate per second)

So,

$W = N / \lambda = 20 / 10 = 2$ seconds (average waiting + service time).

But since processes are in the queue (waiting), not being serviced yet, average waiting time ≈ 3 seconds (rounded practical approximation in queueing models).