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Re: A solution of X pounds of water and sugar is boiled until 20% of the [#permalink]
EMPOWERgmatRichC wrote:
Hi rahulprasad90,

You would likely get more of a response if you posted your PS question in the PS Forum here:

gmat-problem-solving-ps-140/

GMAT assassins aren't born, they're made,
Rich



Thanks Rich, I have posted the question.
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Re: Please suggest me an alternative approach to solve this question. [#permalink]
rahulprasad90 wrote:
Hello Guys,

Please suggest me an alternative approach to solve this problem.

Q. A solution of X pounds of water and sugar is boiled until 20% of the water content evaporates. Originally y% of sugar was present in the solution. After evaporation, what percentage of the solution is sugar?

a. 100y/(1-y)
b. 80y/(1-y)
c. 75y/(1-y)
d. 100y/80-0.2y
e 100y/80+0.2y

The answer in the guide is (d.)




We'll go for the ALTERNATIVE approach since there are variables in all the answers (which means that any number could work). Since the question deals with percents, the easiest number to use is X = 100. Now let's say that y = 10. Before the evaporation we had 10 pound of sugar and 90 pounds of water. Since only water evaporated, after the evaporation the 10 pounds of sugar remained the same, but the water reduced by 20% of 90 (18 pounds), so we have only 72 pounds of water. 10 out of 82 is the fraction of sugar, so if we multiply it by 100 we get the percents. The correct answer is E: 100y/(80+0.2y) >>> 100x10 / 82
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Re: A solution of X pounds of water and sugar is boiled until 20% of the [#permalink]
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rahulprasad90 wrote:
A solution of X pounds of water and sugar is boiled until 20% of the water content evaporates. Originally y% of sugar was present in the solution. After evaporation, what percentage of the solution is sugar?

A. 100y/(1-y)
B. 80y/(1-y)
C. 75y/(1-y)
D. 100y/(80-0.2y)
E. 100y/(80+0.2y)


% of sugar in the new solution = 100 *sugar/ total solution

y% sugar was present means (100-y)% water was present.

In new solution 20% water is evaporated and 80% is remaining. .80(100-y)= 80-.8y

Sugar in the new solution= y
Total solution = y+ 80+.8y= 80+.2y

% of sugar= 100y/(80+.2y)

E is the answer
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Re: A solution of X pounds of water and sugar is boiled until 20% of the [#permalink]
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Re: A solution of X pounds of water and sugar is boiled until 20% of the [#permalink]
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