# Linear Programming Problem

• Jun 21st 2006, 04:44 PM
irishwisteria
Linear Programming Problem
Okay, I am not feeling really well, and this is frustrating me quite a bit. :mad:

Here is the problem:
A manufacturer of refrigerators must ship at least 100 refrigerators to its two West Coast warehouses. Warehouse A holds a maximum of 75 refrigerators and Warehous B holds a maximum of 80 refrigerators. It costs $12 to ship a refrigerator to warehouse A and$10 to ship one to warehouse B. Union rules require that at least 300 workers be hired. Shipping a refrigerator to Warehouse A requires 4 workers, while shipping a refrigerator to Warehouse B requires 2 workers. How many refrigerators should be shipped to each warehouse to minimize costs? What is the minimum cost?

Okay, now here is my problem: Teacher says that there are three constraints and then the objective function. So, I have:

Objective function: c=12x+10y

Constraints: 1. 75x+80y >/= 100
2. 4x + 2y >/= 300

Now, could someone give me a hint as to what I am looking for in the third constraint? I mean I have a constraint for space and workers, what else is there? I have a feeling I am missing something obvious.
• Jun 21st 2006, 05:44 PM
Quick
Quote:

Originally Posted by irishwisteria
Okay, I am not feeling really well, and this is frustrating me quite a bit. :mad:

Here is the problem:
A manufacturer of refrigerators must ship at least 100 refrigerators to its two West Coast warehouses. Warehouse A holds a maximum of 75 refrigerators and Warehous B holds a maximum of 80 refrigerators. It costs $12 to ship a refrigerator to warehouse A and$10 to ship one to warehouse B. Union rules require that at least 300 workers be hired. Shipping a refrigerator to Warehouse A requires 4 workers, while shipping a refrigerator to Warehouse B requires 2 workers. How many refrigerators should be shipped to each warehouse to minimize costs? What is the minimum cost?

Okay, now here is my problem: Teacher says that there are three constraints and then the objective function. So, I have:

Objective function: c=12x+10y

Constraints: 1. 75x+80y >/= 100
2. 4x + 2y >/= 300

Now, could someone give me a hint as to what I am looking for in the third constraint? I mean I have a constraint for space and workers, what else is there? I have a feeling I am missing something obvious.

The area in red is incorrect and should be split into 3 different equations...

$\displaystyle x\leq75$ and $\displaystyle y\leq80$ these two show space constraints
$\displaystyle x+y\geq100$ and this one shows minimum ref. sent
• Jun 21st 2006, 06:06 PM
ThePerfectHacker
$\displaystyle x,y\geq 0$ in the first quadrant
• Jun 21st 2006, 10:13 PM
ticbol
Quote:

Originally Posted by irishwisteria
Okay, I am not feeling really well, and this is frustrating me quite a bit. :mad:

Here is the problem:
A manufacturer of refrigerators must ship at least 100 refrigerators to its two West Coast warehouses. Warehouse A holds a maximum of 75 refrigerators and Warehous B holds a maximum of 80 refrigerators. It costs $12 to ship a refrigerator to warehouse A and$10 to ship one to warehouse B. Union rules require that at least 300 workers be hired. Shipping a refrigerator to Warehouse A requires 4 workers, while shipping a refrigerator to Warehouse B requires 2 workers. How many refrigerators should be shipped to each warehouse to minimize costs? What is the minimum cost?

Okay, now here is my problem: Teacher says that there are three constraints and then the objective function. So, I have:

Objective function: c=12x+10y

Constraints: 1. 75x+80y >/= 100
2. 4x + 2y >/= 300

Now, could someone give me a hint as to what I am looking for in the third constraint? I mean I have a constraint for space and workers, what else is there? I have a feeling I am missing something obvious.

Your teacher should have said there are four constraints:
(You assumed x = number of refs delivered to Warehouse A, and y = number of refs to Warehouse B.)

A manufacturer of refrigerators must ship at least 100 refrigerators to its two West Coast warehouses.
x +y >= 100 ---------------------(1)

Warehouse A holds a maximum of 75 refrigerators...
x <= 75 ------------------(2)

...and Warehous B holds a maximum of 80 refrigerators.
y <= 80 -------------(3)

Union rules require that at least 300 workers be hired. Shipping a refrigerator to Warehouse A requires 4 workers, while shipping a refrigerator to Warehouse B requires 2 workers.
4X +2y >= 300
Or, in its lowest terms,
2x +y >= 150 -------------(4)

Those are the 4 constraints.

--------------------------------------
To solve the question.....

If you plot those on the same x,y coordinates setup, and solve for the intersections of those four inequalities, you will find that the feasible region is a quadrilateral whose vertices are (35,80), (75,80), (75,25) and (50,50).

Testing those 4 corner points against the objective function, you will find that corner (50,50) gives the lowest cost, so, to minimize cost, ship 50 refs to Warehouse A and also 50 refs to Warehouse B.
And the minmum cost will be 50(12) +50(10) = \$1100.
• Jun 22nd 2006, 12:36 AM
JakeD
Quote:

Originally Posted by ticbol
Union rules require that at least 300 workers be hired. Shipping a refrigerator to Warehouse A requires 4 workers, while shipping a refrigerator to Warehouse B requires 2 workers.
4X +2y >= 300
Or, in its lowest terms,
2x +y >= 150 -------------(4)

I don't see how the union rules pose any constraint at all for this problem.

If the shipping requirements for workers are less than 300, then some workers will be idle. There is nothing that says the total number of workers used must be at least 300.

If the shipping requirements for workers exceed 300, the manufacturer can hire more. It says at least 300 must be hired. It does not say the manufacturer cannot hire more.

So the union rules mean nothing here. Thus there are not 4 constraints, but 3 as the teacher says.
• Jun 22nd 2006, 01:57 AM
ticbol
Quote:

Originally Posted by JakeD
I don't see how the union rules pose any constraint at all for this problem.

If the shipping requirements for workers are less than 300, then some workers will be idle. There is nothing that says the total number of workers used must be at least 300.

If the shipping requirements for workers exceed 300, the manufacturer can hire more. It says at least 300 must be hired. It does not say the manufacturer cannot hire more.

So the union rules mean nothing here. Thus there are not 4 constraints, but 3 as the teacher says.

"Union rules require that at least 300 workers be hired. Shipping a refrigerator to Warehouse A requires 4 workers, while shipping a refrigerator to Warehouse B requires 2 workers."

Is there something not English in that Union requirement? Did it specifically say "Union rules require that at least 300 workers must be hired"?

----------------------------
Then, you said :

"If the shipping requirements for workers exceed 300, the manufacturer can hire more. It says at least 300 must be hired. It does not say the manufacturer cannot hire more."

Duh.
Do I understand English? Am I lost here?