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).