SOLUTION: how many pounds of coffee worth 9 dollars a pound should be added to 30 pounds of coffee worth 3 dollars a pound to get a mixture worth 5 dollars a pound?

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Question 465836: how many pounds of coffee worth 9 dollars a pound should be added to 30 pounds of coffee worth 3 dollars a pound to get a mixture worth 5 dollars a pound?
Answer by kingme18(98) About Me  (Show Source):
You can put this solution on YOUR website!
x=number of pounds of $9 coffee

I'm going to multiply each "price per pound" by "number of pounds". Note that our final mixture will have 30+x pounds, since we're adding x pounds in.

$9/pound * x pounds + $3/pound * 30 pounds = $5/pound * (30 + x) pounds

9%2Ax%2B3%2A30=5%2A%2830%2Bx%29 Simplify a bit: 9x%2B90=150%2B5x. Subtract 5x on both sides to bring all the x's together: 4x%2B90=150. Subtract 90 from both sides to get all the numbers together: 4x=60. Divide by 4 on both sides to finish getting x by itself: x=15. Thus, you need to add 15 pounds of $9 coffee.