Determine the number of each grill (super, deluxe) that should be made this week in order to maximize profit?

by Fire Places on June 8, 2010

A foundry makes two types of cast iron fireplace grill: the super grill and the deluxe grill.
Producing one super grill requires 25 kilograms of iron and 25 minutes of labour, while producing one deluxe grill requires 35 kilograms of iron and 20 minutes of labour.
The profit from a super grill is .5 and from a deluxe grill . There are 6,850 kilograms of iron and 95 hours of labour available each week.
As there is a surplus from last week the owner has decided that no more than 150 super grills can be made this week.
Determine the number of each grill (super, deluxe) that should be made this week in order to maximize profit?
How should i use trial and error to find number of each grill?


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{ 2 comments… read them below or add one }

Morewood June 8, 2010 at 5:13 pm

You are studying "linear programming".

You have a number of variables:
Let "x" = the number of super grills to make,
Let "y" = the number of …

You want to maximize the (linear) profit function:
profit = f(x,y) = …

Subject to several constraints:
Amount of iron is at most 6850 kilograms. Write an inequality in x and y.
Amount of labour is at most 95 hours. (How many minutes?) Another inequality.
At most 150 super grills. Yet another inequality, but a very simple one!

Finally some common sense inequalities:
x is greater than or equal 0.
y is greater than or equal 0.

These constraints define a polygon. The maximum will be at a vertex. Since this is only 2 dimensional, it is easy to draw the graphs (on a computer if you are lazy like me) and find the vertices. The gradient of the profit function (if you know what that is) can help determine which vertex will be the maximum. (The gradient tells you in which direction the profit function is increasing. At a maximum point, the gradient must be pointing out of the constraint polygon, making an angle of at least 90 degrees with the edge to both sides. So at a vertex, of which there are only a finite number to check.)

One last complication. You probably want only whole number answers, but some of the vertices are not integral points. In this case, you have to do a little extra "trimming", cutting off non-integral corners from the nearest integral points on each edge.

cheester June 8, 2010 at 5:13 pm

148 super grills and 90 deluxe grills
using exactly 6850kg of iron
and
5500 mins which is less than 95 hours
it has a profit of $3800

i just use trial and error
and knowing that
7super = $87.5 = 175kg = 175mins
5deluxe = $85 = 175kg = 100 mins

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