Need Help with question using Excel Solver

[matt23conley]

I need some help with the following question using excel solver:

A diet is being prepared for college students. The objective is to feed the students at the least amount of cost, but the diet must be between 1800 and 3600 calories. No more than 1400 calories can be starch, and at least 400 calories have to be protein. The varied diet is made of 2 foods: A and B. Food A costs $.75/lb and contains a total of 600 calories, 400 protein and 200 are starch, but no more than 2 pounds of Food A can be used. Food B costs $.15/lb and contains 900 calories, of which 700 are starch, 100 are protein, and 100 are fat.

a.)Write the equations representing this info
b.)Solve the problem using Microsoft Excel Solver

I can't figure out how to make the variables.
I first started with:
X1=calories of starch
X2=calories of protein
X3=calories of fat

then constraints of:
1800<=x1+x2+x3<=3600
x1<=1400
x2>=400

then I can't figure how to apply the other constraints of using only 2 pounds of Food A.

I also can't figure out what the objective function would be.

Please help. Thanks

 

[Glove_Man]

Matt - you're coming at this from the wrong direction. The calories of starch, protein and fat should be outputs, not inputs.

The inputs should be the pounds of Food A used (I named this Alpha) and the pounds of Food B used (Beta).

Then, you can create formulas to represent the total calories of Starch, protein, fat and the overall cost. For example, Cost = 0.75*Alpha + 0.15 *Beta.

The objective is then to minimise the overall cost. The 2 pounds of Food A restraint is satisfied by setting Alpha <= 2.

 

[matt23conley]

Does this look better for constraints:

1800<=Alpha+Beta<=3600
Alpha<=2
200*alpha+700*beta<=1400
400*alpha+100*beta>=400

 

[Glove_Man]

The first one isn't right yet.

The number of calories is 600*Alpha + 900*Beta