Linear programming graphing
Answer:
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Probability of k or More Customers Waiting in Line and/or Being Waited On |
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k |
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0 |
0.667 |
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1 |
0.444 |
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2 |
0.296 |
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3 |
0.198 |
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D6. Calls arrive at Lynn Ann Fish’s hotel switchboard at |
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a rate of 2 per minute. The average time to handle each is 20 seconds. |
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There is only one switchboard operator at the current time. |
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The Poisson and exponential distributions appear to be relevant |
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in this situation. |
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a) What is the probability that the operator is busy? |
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b) What is the average time that a customer must wait before |
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reaching the operator? |
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c) What is the average number of calls waiting to be answered? Answer: |
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D8. Virginia’s Ron McPherson Electronics Corporation |
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retains a service crew to repair machine breakdowns that occur |
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on average l = 3 per 8-hour workday (approximately Poisson in |
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nature). The crew can service an average of m = 8 machines per |
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workday, with a repair time distribution that resembles the exponential |
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distribution. |
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a) What is the utilization rate of this service system? |
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b) What is the average downtime for a broken machine? |
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c) How many machines are waiting to be serviced at any given |
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time? |
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d) What is the probability that more than 1 machine is in the |
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system? The probability that more than 2 are broken and |
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waiting to be repaired or being serviced? More than 3? More |
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than 4? |
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Answer:
M/M/1 model with = 3, = 8
(a) The utilization rate, , is given by:
(b) The average down time, Ws, is the time the machine waits to be serviced plus the time taken to perform the service.
(c) The number of machines waiting to be served, Lq, is, on average:
(d) Probability that more than one machine is in the system:
Probability that more than 2, 3, or 4 machines are in the system:
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B7. The Attaran Corporation manufactures two electrical |
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products: portable air conditioners and portable heaters. The |
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assembly process for each is similar in that both require a certain |
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amount of wiring and drilling. Each air conditioner takes 3 hours |
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of wiring and 2 hours of drilling. Each heater must go through |
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2 hours of wiring and 1 hour of drilling. During the next production |
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period, 240 hours of wiring time are available and up to |
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140 hours of drilling time may be used. Each air conditioner sold |
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yields a profit of $25. Each heater assembled may be sold for a |
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$15 profit. |
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Formulate and solve this LP production-mix situation, and |
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find the best combination of air conditioners and heaters that |
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yields the highest profit.
ANSWER:
Let x1 number of air conditioners to be produced x2 number of heaters to be produced
Maximize 25x1 15x2 Subject to 3x1 2x2 240 (wiring) 2x1 1x2 140 (drilling) x1, x2 0 (non-negativity) Profit: @a: (x1 0, x2 0) Obj $0 @b: (x1 0, x2 120) Obj 25 0 15 120 $1,800 @c: (x1 40, x2 60) Obj 25 40 15 60 $1,900* @d: (x1 70, x2 0) Obj 25 70 15 0 $1,750 * The optimal solution is to produce 40 air conditioners and 60 heaters each period. Profit will be $1,900.
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22
22
(b)
()3(32)3
0.667 time units(minutes)
24
(c) 1.333
()3(32)3
q
q
W
L
l
mml
l
mml
===
--
=
====
--
3
0.375
8
l
r
m
===
(
)
(
)
11
0.2 days, or 1.6 hours
83
s
W
ml
===
--
22
3
0.225 machines waiting
()8(83)
q
L
l
mml
===
--
1
2
1
39
, or 0.141
864
k
nkn
PP
l
m
+
>>
éù
éù
====
êú
êú
ëû
ëû
3
2
4
3
5
4
327
0.053
8512
381
0.020
84096
3243
0.007
832,768
n
n
n
P
P
P
>
>
>
éù
===
êú
ëû
éù
===
êú
ëû
éù
===
êú
ëû
1
+300 ()
2
2
360 ()
3
, 0
SDA
SDB
SD
£
+£
³
22
//1 model: 20, 30
20
2 customers in the system on the average
3020
11
0.1 hour (6 minutes) that the average cu
stomer spends in the total system
3020
20
1.33 cus
()30(3020)
s
s
q
MM
L
W
L
lm
l
ml
ml
l
mml
==
===
--
===
--
===
--
tomers waiting for service in line on th
e average
20
1/15 hour=(4 minutes)=average waiting ti
me of a customer in the queue awaiting s
ervice
()30(3020)
20
=0.67percent of the time that he
30
q
W
l
mml
l
r
m
===
--
===
0
is busy waiting on customers
110.33probability that there are no cust
omers in the system
(being waited on or waiting in the queue
) at any given time
P
l
r
m
=-=-==
l
m
+
>
æö
=
ç÷
èø
1
k
nk
P
180/hour, 120/hour,
//1 model with
or 3/min. and 2/min.
2
(a) 0.667
3
MM
ml
ml
l
r
m
==
==
===