Question

During lunchtime, customers arrive at a postal office at a rate of A = 36 per hour. The interarrival time of the arrival process can be approximated with an exponential distribution. Customers can be served by the postal office at a rate of u = 45 per hour. The system has a single server. The service time for the customers can also be approximated with an exponential distribution.

a. What is the probability that at most 4 customers arrive within a 5-minute period? You can use Excel to calculate P(X<=x). b. What is the probability that the service time will be less than or equal to 30 seconds?

Answer 1

a. To find the probability that at most 4 customers arrive within a 5-minute period, we need to use the Poisson distribution with the parameter λ = A * t, where t is the time period in hours. In this case, t = 5/60 = 1/12 hour. So, λ = 36/12 = 3.

Using Excel, we can calculate P(X <= 4) = POISSON(4,3,TRUE) = 0.2650. Therefore, the probability that at most 4 customers arrive within a 5-minute period is 0.2650.

b. To find the probability that the service time will be less than or equal to 30 seconds, we need to use the exponential distribution with the parameter μ = u/60, where u is the service rate in customers per hour. In this case, μ = 45/60 = 0.75.

Using Excel, we can calculate P(X <= 30) = EXPONDIST(30,0.75,TRUE) = 0.4013. Therefore, the probability that the service time will be less than or equal to 30 seconds is 0.4013.