SOLUTION: A coffee shop decides to make a house blend. She mixes coffee costing 3.00 per pound with coffee costing 5.50 per pound. How many pounds of each coffee does she need to make 40 pou

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Question 711417: A coffee shop decides to make a house blend. She mixes coffee costing 3.00 per pound with coffee costing 5.50 per pound. How many pounds of each coffee does she need to make 40 pounds of the blend costing 4.00 per pound.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = pounds of $3/lb coffee needed
Let +b+ = pounds of $5.50/lb coffee needed
given:
(1) +a+%2B+b+=++40+
(2) +%28+3a+%2B+5.5b+%29+%2F+40+=+4+
--------------------------
(2) +3a+%2B+5.5b+=+160+
(2) +6a+%2B+11b+=+320+
Multiply both sides of (1) by 6
and subtract (1) from (2)
(2) +6a+%2B+11b+=+320+
(1) +-6a+-6b+=+-240+
+5b+=+80+
+b+=+16+
and, since
(1) +a+%2B+b+=++40+
(1) +a+=+24+
24 pounds of $3/lb coffee are needed
16 pounds of $5.50/lb coffee are needed
check:
(2) +%28+3%2A24+%2B+5.5%2A16+%29+%2F+40+=+4+
(2) +%28+72+%2B+88+%29+%2F+40+=+4+
(2) +160+=+4%2A40+
(20 +160+=+160+
OK