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DS question.. x=3y

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Source: — Data Sufficiency |
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hellowww

by ladhanivishal » Sun Jul 05, 2009 11:50 pm
is it really a silly question? does anybody have anything to offer??
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Re: hellowww

by real2008 » Mon Jul 06, 2009 12:18 am
ladhanivishal wrote:is it really a silly question? does anybody have anything to offer??
r u sure the question u have typed is correct?
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by ladhanivishal » Mon Jul 06, 2009 1:30 am
yes.. pretty much.. any clue?
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by hk » Mon Jul 06, 2009 12:28 pm
x=3y means:

1. Both x and y have the same sign => both positive or both negative
or
2. Both are zero

Now the question asked is - Is X^2> y^2? so all we need to know is whether they fall into category 1 or 2. If they fall into category 1. then the answer is Yes and if they fall into category 2 then the answer is No.

1) This says that x+y < x*y

This means that the x and y cannot be a fraction or negative integer or zero.. Which is sufficient to answer the question.

2) x^2 = 9 * y^2

Here x and y can be zero and can satify the equation. In this case the answer to the question would be NO.
But x and y can also be positive integers where x^2 / y^2 = 9 in which case the answer to the main question would be YES. Hence Insufficient!!

So answer is A.
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hk

by deltaforce » Mon Jul 06, 2009 10:41 pm
hey hk

second statement gives us two values

x^2=9y^2

by switching

x^2-9y^2=0

(x-3y)(x+3y) =0

x=-3y, 3y

statement tells us x=3y and not -3y, so 2nd is suff...

dunno if i figured it correctly...

thanks
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