Question 1100387
Average number of calls will be 21, the 3 per hour * 7 hours
In 4 hours, expect 12 calls.
Poisson has parameter 12
e^(-12)*12^5/5!=0.0127
e^(-12)*12^4/4!=0.0053
e^(-12)*12^3/6=0.0018
e^(-12)*144/2=0.0004
e^(-12)*12=0.00007
rounding the last the sum is 0.0203.