The male alpine rabbits of the Tzatzek nature reserve have suffered a

Question

The male alpine rabbits of the Tzatzek nature reserve have suffered a disease that killed 90 of them, causing the male to female ratio to drop from 3:2 to 2:3. How many alpine rabbits lived in the reserve before the disease struck?

A. 180
B. 270
C. 360
D. 450
E. 540

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$!vakumar.m · Answer

The male alpine rabbits of the Tzatzek nature reserve have suffered a disease that killed 90 of them, causing the male to female ratio to drop from 3:2 to 2:3. How many alpine rabbits lived in the reserve before the disease struck?

Let male alpine rabbits be x and female be y
Earlier: male to female ratio was - x/y = 3/2 => 2x = 3y
Later: male to female ratio - (x-90)/y = 2/3
on solving the two equations we get
x = 162 and y = 108 
The number of alpine rabbits that lived in the reserve before the disease struck = x+y = 162+108 = 270
Answer B

twobagels · Answer

\frac{{3*x - 90}}{{2*x}} = \frac{{2*x}}{{3*x}}

3*x - 90 = 2*x

x = 90

Therefore, original number of male rabbits will be 3*x + 90 = 270

szcz · Answer

One of the most important rules of GMAT is to not assumer. Hence, I think the wording of this question needs to be edited. The question does not mention whether the number of female rabbits have remained constant. Due to this there will be 2 cases possible. 
Case 1: 
Number of female rabbits remain constant. In this case the answer will be correct.
Case 2: 
Number of female rabbits number increase.
In this case, since we know the difference between the number of earlier male rabbits and current male rabbits to be 90, we will get the following values. 
Number of earlier rabbits: Male-270, Female-180
Number of current rabbits: Male-180, Female- 270
This will give option D as the correct answer. 
 Bunuel

Regor60 · Answer

Since there is nothing stated about the female rabbits there's no basis for assuming their number would change. So you could just as easily assume their number decreased instead of increased.

Further, your calculation in scenario two makes the assumption that the number of female rabbits increased by the same amount that the number of male rabbits decreased, where in fact it would be unknown under your hypothetical.

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szcz · Answer

I am not assuming anything. If i assumed the number of female rabbits were changing, I would arrive at an answer. The case where the number remains constant would be eliminated. What I have done is listed all the possible cases, which is the normal method for solving quant questions. Thereby arriving at 2 answers. Every GMAT question is precise. There is no space for ambiguity. But in this question you need to assume the number being constant else there are 2 answers possible.

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The male alpine rabbits of the Tzatzek nature reserve have suffered a

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The male alpine rabbits of the Tzatzek nature reserve have suffered a

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