Solution A contains equal amount of alcohol and water in it. It is hea

Question

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

Are You Up For the Challenge: 700 Level Questions

A. 2
B. 4
C. 6
D. 8
E. 12

Are You Up For the Challenge: 700 Level Questions

ThatDudeKnows · Accepted Answer

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!

Kartika09 · Answer

Hi  ThatDudeKnows

Is it ok for us to assume that the level of alcohol in solution A remains unchanged?

Also, in general, for questions like these, unless the effect on variable y is specifically mentioned, do we assume it to be the same?

ThatDudeKnows · Answer

Kartika09

Good question! This is absolutely the type of thinking that will be necessary on DS, CR, and RC, so awesome that you're training your brain to think this way! On PS, it comes into play sometimes, but on this question, the only way to arrive at an answer is to keep the unspecified variables static. This isn't an official question and GMAC is pretty good about clearing ambiguities, so I wouldn't sweat the concept too much here; definitely keep watching for it on those other question types!

MonishBhawale · Answer

assuming values (note the solution B AL:water ratio is 3:2 , so assume value of water in solution A to be divisible by 5
solution A
AL:water t
10:10
50% water evaporate
10:5
solution b = the reduced volume of water ie 5
so AL : Water
2:3
mixing both
alcohol : Water
12:8
to make them 50 :50
add 4 water
so answer 4

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Solution A contains equal amount of alcohol and water in it. It is hea

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Solution A contains equal amount of alcohol and water in it. It is hea

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