SOLUTION: In testing gasohol mixtures, two mixtures are on hand: Mixture A (90% gasoline, 10% alcohol) and mixture B (80% gasoline, 20% alcohol). How much of each mixture must be combined to

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Question 475262: In testing gasohol mixtures, two mixtures are on hand: Mixture A (90% gasoline, 10% alcohol) and mixture B (80% gasoline, 20% alcohol). How much of each mixture must be combined to get 100 gallons of an 84% gasoline, 16% alcohol mixture.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = gallons of mixture A needed
Let b = gallons of mixture B needed
In words:
(gallons of gasoline in final mixture) / (gallons of final mixture) = 84%
given:
(1) +a+%2B+b+=+100+
(2) +%28.9a+%2B+.8b%29+%2F+100+=+.84+
-----------------
From (2),
(2) +.9a+%2B+.8b+=+84+
(2) +9a+%2B+8b+=+840+
Multiply both sides of (1) by 8 and subtract from (2)
(2) +9a+%2B+8b+=+840+
(1) +-8a+-+8b+=+-800+
+a+=+40+
and
(1) +a+%2B+b+=+100+
(1) +40+%2B+b+=+100+
(1) +b+=+60+
40 gallons of mixture A must be added to 60 gallons of mixture B
check answer:
(2) +%28.9a+%2B+.8b%29+%2F+100+=+.84+
(2) +%28.9%2A40+%2B+.8%2A60%29+%2F+100+=+.84+
(2) +%28+36+%2B+48+%29+%2F+100+=+.84+
(2) +84%2F100+=+.84+
OK