Q76.Marks: +2.0UGC NET Paper 2: Computer Science and Application 26th June 2025 Shift 1
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?
1.03 seconds
2.02 seconds✓ Correct
3.18 seconds
4.09 seconds
Solution
The correct answer isOption 2) 2 seconds
Key Idea (Little’s Law)
For a stable queueing system: L = λ × W, where
L = average number of jobs in the system/queue,
λ = average arrival rate (jobs per second),
W = average time a job spends in the system/queue (seconds).
When we are given the queue length (not including service), we use the queue version: Lq = λ × Wq.
Given
Average arrival rate: λ = 10 processes/second.
Average number of processes waiting in the queue: Lq = 20.
Compute the average waiting time in queue
Wq = Lq / λ = 20 / 10 = 2 seconds
Therefore, the average waiting time per process is 2 seconds.
Notes
This uses Little’s Law and assumes the system is in steady state.
We were asked for waiting time in the queue only; service time (CPU time) is not included.