I think his has to do with arrival time distributions, but correct me if I am wrong. Here’s the question:
5 erlangs are offered to 15 circuits for half an hour followed by 15 erlangs in the next half hour. Using the Erlang-B formula (and thereby assuming equilibrium conditions in each half hour slot) calculate the blocking probabilities in each half hour. Assume that the mean call holding time is 3 minutes. Use these values to estimate the probability that a randomly chosen call in the 1 hour period is blocked and compare this with the blocking when 10 erlangs is offered to 15 circuits.