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Problem found in math online lab regarding yes/no DS

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angs316
 Post subject: Problem found in math online lab regarding yes/no DS
 Post Posted: Thu Aug 11, 2011 4:25 am 
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Course Students


Posts: 1
Source Online Lab Yes/No DS

If x is a positive integer, is sqrt (x) an integer?
1. sqrt(4x) is an integer
2. sqrt(3x) is not an integer

If we take x= 1/4 you will notice that this satisfies the criteria in the question and no.1 however sqrt(1/4) is not an integer.
Thus answer a is insufficient.

The online lab claims answer choice (A) to be correct. I believe this is wrong. Am i correct?
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mithunsam
 Post subject: Re: Problem found in math online lab regarding yes/no DS
 Post Posted: Thu Aug 11, 2011 12:55 pm 
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Course Students


Posts: 76
The quesiton specifically states that x is a +ve integer. So, you cannot substitute x=1/4

For statement 1 to be true, x has to be a perfect square (like 1, 4, 9 etc). Therefore, statement 1 is sufficient.


Last edited by mithunsam on Thu Aug 11, 2011 2:54 pm, edited 1 time in total.

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aalokshah85
 Post subject: Re: Problem found in math online lab regarding yes/no DS
 Post Posted: Thu Aug 11, 2011 1:20 pm 
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Students


Posts: 6
angs316 wrote:
Source Online Lab Yes/No DS

If x is a positive integer, is sqrt (x) an integer?
1. sqrt(4x) is an integer
2. sqrt(3x) is not an integer

If we take x= 1/4 you will notice that this satisfies the criteria in the question and no.1 however sqrt(1/4) is not an integer.
Thus answer a is insufficient.

The online lab claims answer choice (A) to be correct. I believe this is wrong. Am i correct?


The question states that x is a POSITIVE INTEGER

Statement 1: States sqrt (4x) is an integer - this is sufficient 4 - is a perfect square (2*2) in order for root of 4x to be an integer, x must also be a perfect square (the square root of which must be an integer) you can also take examples (such as 9)

Statement 2: States sqrt(3x) is not an integer - Not sufficient - x could be 9 (3*3) or anyother perfect square (in which case DS answer is Yes) thus 3x = 27 or x could be 7 or any other number that is not a perfect Square (in which case DS answer is No)

Ans: (a)
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RonPurewal
 Post subject: Re: Problem found in math online lab regarding yes/no DS
 Post Posted: Fri Aug 12, 2011 3:44 am 
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ManhattanGMAT Staff


Posts: 7146
hi -- this is the wrong folder for this question; this folder is for GMAT PREP SOFTWARE PROBLEMS ONLY.

if you wish to post this problem, please post it in the MGMAT CAT or GENERAL MATH folder.
thank you.

this thread is locked and will be deleted in about 1 week; if you wish to continue the discussion, please post a new thread in the correct folder.
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