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Acid solution

by GmatKiss » Sat May 26, 2012 10:54 pm
Some part of a 50% solution of acid was replaced with an equal amount of 30% solution of acid. If, as a result, 40% solution of acid was obtained, what part of the original solution was replaced?

1/5

1/4

2/3

1/2

4/5
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by Anurag@Gurome » Sun May 27, 2012 1:22 am
GmatKiss wrote:Some part of a 50% solution of acid was replaced with an equal amount of 30% solution of acid. If, as a result, 40% solution of acid was obtained, what part of the original solution was replaced?
Intuitive Approach:
Just observe that the concentration of the final solution (40%) is exactly at the middle of the concentrations of the solutions mixed together (50% and 30%).

Hence, exactly same amount of both solutions were mixed together, i.e. 1/2 of the original solution was replaced.

The correct answer is D.
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by Anurag@Gurome » Sun May 27, 2012 1:23 am
Algebraic Approach:
Say, x part of 50% solution was replaced with x part of 30% solution.

So, (1 - x)*50 + x*30 = 40
--> 50 - 50x + 30x = 40
--> 20x = 10
--> x = 1/2

The correct answer is D.
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