Calculate the blocking probably Pb in 100 line strowger switching system where 10 calls are in progress and 11th one arrives, probably that there is a call in a given decade = 1/10 and probably that another call is destined to same decade but not to same number = 9/98.
Probability that there is a call in a given decade =10/100
Probability that other call is destined to the same decade but not to same number =
9/98
Therefore, the blocking probability = (1/10)*(9/98)
= 0.009 Ans