SOLUTION: Gus has on hand 5% alcohol solution and a 20% alcohol solution. He needs 30 liters of 10% alcohol solution. How many liters of each solution should he mix together to obtain the mi

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Question 720623: Gus has on hand 5% alcohol solution and a 20% alcohol solution. He needs 30 liters of 10% alcohol solution. How many liters of each solution should he mix together to obtain the mixture he needs?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = liters of 5% solution needed
Let +b+ = liters of 20% solution needed
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(1) +a+%2B+b+=+30+
(2) +%28+.05a+%2B+.2b+%29+%2F+30+=+.1+
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(2) +.05a+%2B+.2b+=+3+
(2) +5a+%2B+20b+=+300+
Multiply both sides of (1) by +5+ and
subtract (1) from (2)
(2) +5a+%2B+20b+=+300+
(1) +-5a+-+5b+=+-150+
+15b+=+150+
+b+=+10+
and, since
(1) +a+%2B+b+=+30+
(1) +a+=+20+
20 liters of 5% solution are needed
10 liters of 20% solution are needed
check answer:
(2) +%28+.05%2A20+%2B+.2%2A10+%29+%2F+30+=+.1+
(2) +%28+1%2B+2+%29+%2F+30+=+.1+
(2) +3%2F30+=+.1+
(2) +3+=+3+
OK