<PRE><B>Question 567606</B>
A merchant has coffee worth $4 a pound that she wishes to mix with 80 pounds of coffee worth $9 a pound to get a mixture that can be sold for $5 a pound. How many pounds of the $4 coffee should be used? 
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You would be correct!
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Let x = amount (pounds) of $4 coffee
then
4x + 9(80) = 5(x+80)
4x + 720 = 5x+400
720 = x+400
320 pounds = x
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