SOLUTION: How much water must be added to 12 L of a 40% solution of alcohol to obtain a 30% solution?

Question 535257: How much water must be added to 12 L of a 40% solution of alcohol to obtain a 30% solution?

Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!
I will pretend that I am not a chemist, because from the point of view of a chemist, this problem is so wrong on multiple levels that it makes me want to cry.
Let the volume of water that must be added be .
The amount of alcohol in the solution is 40% of 12L, or

If that amount is to be 30% of the expected volume (in liters) of ,
then
--> --> -->
You need to add 4.0L water.
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