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M24 #4

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Re: M24 #4 [#permalink] New post 02 Jul 2012, 23:19
Dce25 wrote:
Let the amount of acid in 80 gram solution(acid+water) be m grams:
So concentration= [m][/80]

water added = x gram
So new conc. = [m][/80+x]

Now Acc. to question [m][/80+x] = [1][/y] of [m][/80]

Solving we get: 80y = 80+x

Therefore each statement is sufficient.

Answer should be (D)


I believe that you have made incorrect inferences. The question stem ask about figuring out the original concentration of the acid. In other words, you have to figure out m.
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Re: M24 #4 [#permalink] New post 02 Jul 2012, 23:24
Dce25 wrote:
Let the amount of acid in 80 gram solution(acid+water) be m grams:
So concentration= [m][/80]

water added = x gram
So new conc. = [m][/80+x]

Now Acc. to question [m][/80+x] = [1][/y] of [m][/80]

Solving we get: 80y = 80+x

Therefore each statement is sufficient.

Answer should be (D)


In Data sufficiency questions, its is exceptionally important to remain focused on what is being asked. AS per the question stem, What was the concentration of acid in the original solution?.
In other words, as per the variables that you have used, one is asked to figure out m/80.
Knowledge of "x" and "y" doesn't help us in achieving this objective
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Re: M24 #4 [#permalink] New post 31 Aug 2012, 19:23
Took the approach of setting up equations and then substituting the given values. Either statement individually is not sufficient since there are 2 variables X and Y.

Considering both the statements together, we get

Total weight of the new solution = 80+X = 80+80 =160

New concentration of acid = (1/Y) = 1/2

Since initial concentration of neither the water nor the acid is given we will be unable to solve the equations. Eg. if initial concentration of acid was say 40 gms then new concentration will be 20 whereas if initial conc of acid was 60 then new would be 30.

Thus I chose the statement E as the answer. Took me a minute and a half though. Will work on improving my speed.
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Re: M24 #4 [#permalink] New post 02 Jul 2013, 08:36
Hoping that Bunuel posts an explanation soon.
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Re: M24 #4 [#permalink] New post 02 Jul 2013, 10:21
Expert's post
Re: M24 #4   [#permalink] 02 Jul 2013, 10:21
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M24 #4

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