SOLUTION: You need a 80% alcohol solution. On hand, you have a 60 mL of a 5% alcohol mixture. How much pure alcohol will you need to add to obtain the desired solution?

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Question 1099061: You need a 80% alcohol solution. On hand, you have a 60 mL of a 5% alcohol mixture. How much pure alcohol will you need to add to obtain the desired solution?
Found 2 solutions by josgarithmetic, josmiceli:
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
x, how much of 100% alcohol
(assuming percent is mass per volume)

%28alcoholContent%29%2F%28totalMixture%29=fractionAsAlcohol

%285%2A60%2B100x%29%2F%28x%2B60%29=80----solve for x.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = mL of pure alcohol needed
+.05%2A60+=+3+ mL of alcohol in the 5% mixture
--------------------------------------------
+%28+x+%2B+3+%29+%2F+%28+x+%2B+60+%29+=+.8+
+x+%2B+3+=+.8%2A%28+x+%2B+60+%29+
+x+%2B+3+=+.8x+%2B+48+
+.2x+=+45+
+x+=+225+
225 mL of pure alcohol should be added
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check answer:
+%28+x+%2B+3+%29+%2F+%28+x+%2B+60+%29+=+.8+
+%28+225+%2B+3+%29+%2F+%28+225+%2B+60+%29+=+.8+
+228+%2F+285+=+.8+
+228+=+.8%2A285+
+228+=+228+
OK