SOLUTION: How many liters of pure water should be mixed with a 9-L solution of 90% acid to produce a mixture that is 50% water?

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Question 899506: How many liters of pure water should be mixed with a 9-L solution of 90% acid to produce a mixture that is 50% water?
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
1*x+0.1*9=0.5(9+x)
1*x+0.9=4.5+0.5x
1x-0.5x=4.5-0.9
0.5x=3.6
x=7.2
check
1*7.2+0.1*9=0.5(9+7.2)
7.2+0.9=0.5(16.2)
8.1=8.1
ok