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605-655 Level|   Mixture Problems|               
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Answer:C
Took time to solve this one, the statement 2 kilograms of solution Y are added to the remaining 6 kilograms of liquid was confusing to me. After thinking more deeply, it was clear to me that new 2 kg of solution Y will also be 30% liquid X and 70% water, and then I was able to get the answer. That was a bit tricky and nice question.
Kudos +1 for posting the question :)
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Initially you start with 8kg of solution which has 2.4kg of X and 5.6kg of water
Post evaporation : 2.4kg of X and 3.6kg of water
Now we add back 2kg of Y --> 1.4Kg water + 0.6Kg X
So we have left 5Kg Water & 3Kg X

Percentage concentration is (3/5)*100 or 37.5%
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rtaha2412
Solution Y is 30 percent liquid X and 70 percent water. If 2 kilograms of water evaporate from 8 kilograms of solutions Y and 2 kilograms of solution Y are added to the remaining 6 kilograms of liquid, what percent of this new liquid solution is liquid X?

A. 30%
B. 33 1/3%
C. 37 1/2%
D. 40%
E. 50%

The best way to solve these problems is to take one step at a time

Initial:
8 kg Solution Y
This means Solution X = 2.4 kg, Water = 5.6 kg

Step 2:
2 kg of water is evaporated.
Left over: Solution X = 2.4 kg and Water = 3.6 kg

Step 3:
2 kg of Solutoin Y is added
Or, 0.6 kg of Solution X and 1.4 kg of water is added

Final:
Solution X = 3, Water = 5
% of solution X = 3/8 * 100 = 37.5%

Option C
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30% of 8 + 30% of 2 = 3 = X
X/T= 3/8 = 0.375 =37.5%

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rtaha2412
Solution Y is 30 percent liquid X and 70 percent water. If 2 kilograms of water evaporate from 8 kilograms of solutions Y and 2 kilograms of solution Y are added to the remaining 6 kilograms of liquid, what percent of this new liquid solution is liquid X?

A. 30%
B. 33 1/3%
C. 37 1/2%
D. 40%
E. 50%

 
Originally, solution Y has 0.3 x 8 = 2.4 kg of liquid X and 0.7 x 8 = 5.6 kg of water. After 2 kg of water evaporate, solution Y has 2.4 kg of liquid X and 3.6 kg of water. However, since 2 kg of solution Y (of which, 0.3 x 2 = 0.6 kg is liquid X and 0.7 x 2 = 1.4 kg is water) are added back to the remaining 6 kilograms of solution Y, solution Y now has 2.4 + 0.6 = 3 kg of liquid X and 3.6 + 1.4 = 5 kg of water). Therefore, the percent of the new solution is liquid X is 3/(3 + 5) = 3/8 = 37.5%.

Answer: C­
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Concept: The question tests on Percentage and comprehension of the question and its inputs.
Solution:

Solution Y:
Liquid X =30% AND Water = 70%

8 Kg of Solution Y is taken and 2kg of Water evaporates from this.

=>8kg of Y has 30%of 8kg=2.4 kg of liquid X originally in it

2kg of Y that evaporated had 30% of 2kg or 0.6kg of liquid X in it

The same is added back

=>0.6 kg of liquid X that evaporated is added back to Y

Q. stem- We have to calculate the new percentage of liquid X in this solution(originally it was 30%)

This should be the "new" weight of liquid X in the solution/ Total weight of the solution *100

=(2.4+0.6) / 8

=3/8 *100

= 37.5% (option c)

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I read somewhere that key to solving such questions quickly is to calculate only the ratio or the weight of the ingredient of interest, which for this particular question is liquid X.

The question is asking for the ratio of liquid X to the total solution.

Old solution:
30% of liquid X in 8 kilos of solution = 2.4 kilos

New solution that is being added to old solution:
30% of liquid X in 2 kilos of solution = 0.6 kilos

Liquid X in final solution: 2.4+0.6 = 3 kilos
Total amount of final solution: 8 - 2 + 2 = 8 kilos

3/8 = 37.5
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Way to go GMAC, making this problem needlessly confusing when they could've just precised that they add back 2 kgs of the original Y solution.
Somehow quant reasoning skills include deciphering confusing prompts... BS
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­Don't even worry about the water. Keep track of how much liquid x you add and you know the total is going back to 8 kg:

­
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