SOLUTION: A coffee merchant combines coffee costing $6 per pound with coffee cost $3.50 per pound. How many pounds of each should be used to make 50lb of a blend costing $4.20 per pound?

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Question 755849: A coffee merchant combines coffee costing $6 per pound with coffee cost $3.50 per pound. How many pounds of each should be used to make 50lb of a blend costing $4.20 per pound?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = pounds of $6/pound coffee needed
Let +b+ = pounds of $3.50/pound coffee needed
+6a+ = cost of $6/pound coffee in blend
+3.5b+ = cost of $3.50/pound coffee in blend
----------------
(1) +a+%2B+b+=+50+
(2) +%28+6a+%2B+3.5b+%29+%2F+50+=+4.2+
----------------------------
(2) ++6a+%2B+3.5b+=+4.2%2A50+
(2) ++60a+%2B+35b+=+2100+
Multiply both sides of (1) by
+35+ and subtract (1) from (2)
(2) ++60a+%2B+35b+=+2100+
(1) +-35a+-+35b+=+-1750+
+25a+=+350+
+a+=+14+
and, since
(1) +a+%2B+b+=+50+
(1) +14+%2B+b+=+50+
(1) +b+=+36+
14 pounds of $6/pound coffee are needed
36 pounds of $3.50/pound coffee are needed
check:
(2) +%28+6a+%2B+3.5b+%29+%2F+50+=+4.2+
(2) +%28+6%2A14+%2B+3.5%2A36+%29+%2F+50+=+4.2+
(2) +%28+84+%2B+126+%29+%2F+50+=+4.2+
(2) +210+=+4.2%2A50+
(2) +210+=+210+
OK