SOLUTION: How many ounces of a solution that is 90% alcohol need to be mixed with 5 ounces of a solution that is 50% alcohol in order to obtain a solution that is 80% alcohol? I have trie

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Question 568850: How many ounces of a solution that is 90% alcohol need to be mixed with 5 ounces of a solution that is 50% alcohol in order to obtain a solution that is 80% alcohol?
I have tried a formula: 5(.50) + x(.90) = .80, but the answer yields a negative amount of ounces which is not possible.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = ounces of 90% solution needed
+.9x+ = ounces of alcohol in 90% solution
+.5%2A5+=+2.5+ ounces of alcohol in 50% solution
given:
+%28+.9x+%2B+2.5+%29+%2F+%28+x+%2B+5+%29+=+.8+
+.9x+%2B+2.5+=+.8%2A%28+x+%2B+5+%29+
+.9x+%2B+2.5+=+.8x+%2B+4+
+.1x+=+1.5+
+x+=+15+
15 ounces of 90% solution are needed
check answer:
+%28+.9%2A15+%2B+2.5+%29+%2F+%28+15+%2B+5+%29+=+.8+
+%28+13.5+%2B+2.5+%29+%2F+20+=+.8+
+16+=+.8%2A20+
+16+=+16+
OK