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a study-aid desk staffed by a graduate student has been established to answer students ‘questions and help in working problems in your OSCM course. The desk is staffed eight hours per day. The dean wants to know how the facility is working. Statistics show that students arrive at a rate of four per hour and the distribution is approximately Poisson. Assistance time averages 10 minutes, distributed exponentially. Assume population and line length can be infinite and queue discipline is FCFS.

a. Calculate the percentage utilization of the graduate student.

b. Calculate the average number of students in the system, excluding the graduate student service.

c. Calculate the average time in the system.

d. Calculate the probability of four or more students being in line or being served.

e. Before a test, the arrival of students increases to six per hour on average. What will the new average line length be?

Short Answer

Expert verified

Assume customer arrival is Poisson distributed and service is exponentially distributed.

Arrival rate = 4 per hour

Service rate, μ = 1 in 10 min = 6 per hour

Step by step solution

01

Step by Step Solution  Step 1: (a) Percentage utilization of the graduate is

Average time utilization P=λμWhere,

P = Average time utilization

μ = Rate of service delivery

λ = Rate of students' arrival

Now, putting these values in the equation for obtaining the following results:

P=46= 0.66 or 66.67% of the time

Hence, the average time utilization of the clerk is 0.667 or 66.67% of the time.

02

(b) The average number of students in the system, excluding the graduate student's Average number of students in the system is

Lq=λ2μ×μ-λ

Where

μ=Rate of service delivery

λ= Rate of students' arrival

Now, substitute the above values in the equation for obtaining the following results:

Lq=426×6-4=1.333students

Hence, the average number of students in the system, excluding the graduate student is1.333

03

(c) the average time in the system is

Average time in the system Ws= Lsλ

=λμ-λλ

Here, μ= 6 and λ= 4 Substitute the above values in the equation for obtaining the following result:

role="math" localid="1650877079217" Ws=46-44=0.5houror30min.

Hence, the average time spent in the system is 30 min.

04

(d) the probability of four or more students in the system is

The probability of four or more students in the system is

P = (1 probability of fewer than 4 students in the system)

P=1-P0+P1+P2+P3

Pn(Probability of n systems in the system) =1-λμλμn

μ = Rate of service delivery

2 = Rate of customers' arrival

Therefore, at

n =0,

P0=0.3333P1=0.2222P2=0.1481

At n= 3, P3=0.0987

Now, substitute the above values in equation (4) to obtain the following results:

P=1-(0.3333+0.2222+0.1481+0.0987)

P=0.1975

Hence, the probability of four or more students in the system is

05

(e) The average line length is

LS=λμ-λ

Where,

Ls= Average line length

λ= Rate of students' arrival

μ= Rate of service delivery

Here? = 6 per hour and μ = 6 per hour now, substitute the above values in the equation to obtain the following results:

LS=66-6=60=∞

Hence, it can be concluded that at? = 6 per hr. the arrival rate would be equivalent to the service rate.

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