SOLUTION: Hi there, I have a quiz tommorow on Substitution and Elimination. I know how to do both, but sadly I am not the sharpest when it comes to word problems. I am stuck with this one.

Question 846857: Hi there, I have a quiz tommorow on Substitution and Elimination. I know how to do both, but sadly I am not the sharpest when it comes to word problems. I am stuck with this one.
Mrs. Lincoln mixes two brands of coffee to make 15 pounds of a mixture selling for $4.78 per pound. She mixes monson coffee selling at 3.90 per pound, with Valley Brothers coffee selling at $5.75 per pound. How many pounds of each coffee should she use in the mixture.
The part I get confused at is how you can mix the two but get something worth less. It would be ideal to get this as soon as possible if not that is ok, I respect your time and do not wish to waste it. Thanks in advance
Found 2 solutions by josgarithmetic, Alan3354:
Answer by josgarithmetic(39618) (Show Source): You can put this solution on YOUR website!
The mixing is NOT making a mixture which costs less. The mixture gives a result which will cost a value BETWEEN the costs of the two different coffees.

LOOK!
Monsoon Coffee___________3.90 dollars per pound
Mixture__________________4.78 dollars per pound
Valley Brothers__________5.75 dollars per pound

The mixture is made mixing the Monsoon coffee with the Valley Brothers coffee.
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
Mrs. Lincoln mixes two brands of coffee to make 15 pounds of a mixture selling for $4.78 per pound. She mixes monson coffee selling at 3.90 per pound, with Valley Brothers coffee selling at $5.75 per pound. How many pounds of each coffee should she use in the mixture.
------------------------
t = amount of $3.90
f = amount of $5.75
====================
t + f = 15 (total coffee)
t*390 + f*575 = 15*478 (total price)
----------
f = 15 - t
390t + 575f = 7170
78t + 115f = 1434
78t + 115*(15-t) = 1434
etc

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