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

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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) About Me  (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 x.
The amount of alcohol in the solution is 40% of 12L, or
0.40%2A12L=4.8L
If that amount is to be 30% of the expected volume (in liters) of 12%2Bx,
then 0.30%2A%2812%2Bx%29=4.8
3.6%2B0.30x=4.8 --> 0.30x=1.2 -->x=1.2%2F0.30 --> x=4.0
You need to add 4.0L water.