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DS question: Instructor, can you please clear this doubt?

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DS question: Instructor, can you please clear this doubt?

by jrikhraj » Sat Sep 11, 2010 7:45 am
What is the ratio of y to x?

(1) y = 3x

(2) x = 11

Can we divide the equation in (1) by x to get the ratio as 3 even if we are not explicitly given that x!=0?

The OA is A. However, I marked C since we were not given that x is !=0.

Instructor, please clear this doubt so that I don't get confused in such an easy problem again !
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by Ian Stewart » Sat Sep 11, 2010 7:58 am
jrikhraj wrote:What is the ratio of y to x?

(1) y = 3x

(2) x = 11

Can we divide the equation in (1) by x to get the ratio as 3 even if we are not explicitly given that x!=0?

The OA is A. However, I marked C since we were not given that x is !=0.

Instructor, please clear this doubt so that I don't get confused in such an easy problem again !
If this were a real GMAT question, they would tell you in advance that x and y are positive. As you've presented the question, I suppose the right answer ought to be C, because, as you point out, x and y could be zero using statement 1 alone, in which case the ratio would be undefined. You'd never need to worry about an exception like that on a real GMAT question however.
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by Aman verma » Sat Sep 11, 2010 8:18 am
Yes , Ian has rightly pointed out that on the actual GMAT, the question will mention whether x & y are positive. And , even if we are not explicitly given x! = 0 , if we assume x!=0 , then from the first statement we get a ratio which becomes undefined. So, following Ian's logic , the answer IMOC.
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by jrikhraj » Sat Sep 11, 2010 10:46 am
Thanks Ian and Aman

This was a question from one of Manhattan's practice GMAT tests so I assumed that it would be very similar to the real GMAT. Even I was very surprised to see that x>0 was not provided. Anyway, i would take it that my reasoning is correct.

Thanks for the quick reply !!
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