SOLUTION: Manha wants to make a 36 percent acid solution. She has already 3 leters of a 72 percent acid solution. How many litres of a 9 percent acid solution must she add.

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Question 993897: Manha wants to make a 36 percent acid solution. She has already 3 leters of a 72 percent acid solution. How many litres of a 9 percent acid solution must she add.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+.72%2A3+=+2.16+ = liters of acid in 72% solution
Let +x+ = liters of 9% solution needed
+.09x+ = liters of acid in 9% solution
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+%28+2.16+%2B+.09x+%29+%2F+%28+3+%2B+x+%29+=+.36+
+2.16+%2B+.09x+=+.36%2A%28+3+%2B+x+%29+
+2.16+%2B+.09x+=+1.08+%2B+.36x+
+.27x+=+1.08+
+x+=+4+
4 liters of 9% solution are needed
check:
+%28+2.16+%2B+.09x+%29+%2F+%28+3+%2B+x+%29+=+.36+
+%28+2.16+%2B+.09%2A4+%29+%2F+%28+3+%2B+4+%29+=+.36+
++2.16+%2B+.36+=+.36%2A7+
+2.52+=+2.52+
OK