In: Statistics and Probability
The Westland Title Insurance Company has a copying machine that is used by the 8 agents at their office. Each agent needs to use the machine 2 times every hour on average and uses it for an average of 4 minutes. Assume the interarrival times and copying times are exponentially distributed.
Arrival rate: λ = 2/60 = 0.033 minutes
Service rate: µ = 1/4 = 0.25 minutes
No. of agents = 8
a) What is the probability that a person arriving to use the machine will find it idle?
P0 = 1 − ρ = 1-(λ/µ) = 1-(0.033/0.25) = 0.868
b) What is the utilization of this machine?
ρ = λ/µ = 0.033/0.25 = 0.132
c) On average, how long will a person have to wait before getting to use the machine?
Waiting time to use the machine = Wq = Lq/λ
Lq = ρ2/(1 − ρ) = 0.8682/(1-0.868) = 5.71
Wq = 5.71/0.033 = 172.96 minutes
d) What is the probability at least 2 agents will be in line waiting for their turn to use the machine?
n = 2
Pn: Probability of n customers in waiting = (1 − ρ)/ρn
P2 = (1-0.868)/0.8682 = 0.175
e) On average how many agents will be waiting to use the machine?
Lq = ρ2/(1 − ρ) = 0.8682/(1-0.868) = 5.71 ~ 6
f) Suppose that the people who use the copy machine are paid an average of $30 per hour. The company is worried about the loss of productivity. It will cost $15 per hour to rent another copy machine. Should it rent another machine?
Average time spent by agent = 1/(µ-λ) = 1/(0.25-.033) = 4.61 minutes
Curent cost = 4.61 * (30/60) * 8 = 18.44 (8 agents)
Cost of new copy machine = 8*4.61*(15/60) = 9.22
Yes, it should rent another machine