<PRE><B>Question 846857</B>
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. 
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t = amount of $3.90
f = amount of $5.75
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t + f = 15 (total coffee)
t*390 + f*575 = 15*478 (total price)
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f = 15 - t
390t + 575f = 7170
78t + 115f = 1434
78t + 115*(15-t) = 1434
etc

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