Bunuel wrote:
Solution A contains equal amount of alcohol and water in it. It is heated till 50 percent of the water in solution A evaporates. Solution B, whose volume is equal to the reduced volume of water in Solution A, is then added to Solution A and the volume of alcohol in the resultant solution is equal to 12 liters. If solution B contains alcohol and water in the ratio 2:3, how many more liters of water should be added to the resultant solution to increase the concentration of water in the resultant solution to 50 percent?
A. 2
B. 4
C. 6
D. 8
E. 12
Let's make x the amount of water in Solution A. We can fill in the grid attached.
We have 2.4x of alcohol and 1.6x of water, so we need 0.8x additional water.
2.4x is 12 and we're trying to add 1/3rd of that, so 4.
Answer choice B.
I'll note that even if you have no idea how to get to the correct answer on this one, you may be able to at least eliminate two answer choices. We are told that there are 12L of alcohol. In order to end up with the same amount of water, we need a total of 12L of water. We already have some water, so answer choice E is out. We have a decent amount of water in both solutions (33% water in A and 60% water in B). If it were all 33%, D would be right, but we have more than that, so answer choice D is out. 1-out-of-3 is better than 1-out-of-5!
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