C) Multiple-Server Model (20 points). Benny the Barber owns a two-chair shop wit
ID: 392234 • Letter: C
Question
C) Multiple-Server Model (20 points). Benny the Barber owns a two-chair shop with two hair stylists. Benny estimates that his customers exhibit a Poisson arrival distribution and that his two hair stylists provide an exponential service distribution. His survey of his shop indicated that customers arrive at a rate of two per hour and his stylists take an average of 20 minutes to give one haircut. Find the following operating characteristics of Benny's queuing system: 1. probability of zero customers in the system 2. probability of more than 2 customers in the system 3. average number of customers in the system 4. average number of customers waiting in line 5. average total time spent in the system including both service time and wait time (per car) 6. average waiting time in line (per customer) 7. utilization of the stylistsExplanation / Answer
Given,
M|M|2 model
Arrival rate (l) = 30 ,ims
Service rate (m)= 20 mins per
Servers (s)= 2
1. Utilization p= l/sm = 30/(2*20)= 30/40 =0.75
Also l/m= 30/20 = 1.5
2. Probability that no customer is in system Po= [(1.5)^0/0! + (1.5)^1/1! + (1.5)^2/2! (1/(1-0.75))]^-1 = 0.142
3. Average number of customers in line Lq= Po (l/m)^s*0.75/ (2)!(1-0.75)^2 =
=(0.142*(1.5^2)*0.75) / (2*(0.25^2)) = 0.239/0.125 = 1.912 persons
4. Average waiting time in line Wq=Lq/l = 1.912/30 = 0.0637 hr = 3.824 mins
5. Average waiting time in system W= Wq+ (1/m) = 0.0637 + (1/20) = 0.1137 hr = 6.822 mins
6. Average number of customers in system L= l*W = 30*0.1137 = 3.411 persons
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