Question 1164359
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A coffee merchant combines coffee that costs $7 per pound with coffee that costs $3.30 per pound. How many pounds of each should be used to make 25 lb of a blend costing $5.89 per pound?
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$H, the more expensive priced coffee
$L, the lower priced coffee
M, how much of the blend to prepare
T, the expected price of the blend
w, the amount of the expensive coffee to use


Accounting for the cost of the blend,
{{{L(M-w)+Hw=TM}}}
-
{{{LM-Lw+Hw=TM}}}
{{{Hw-Lw+LM=TM}}}
{{{w(H-L)=TM-LM}}}

{{{highlight(w=M((T-L)/(H-L)))}}}
Substitute the values given in your description.  The fraction part may be easy to compute.  w can be calculated and then M-w can be evaluated.