Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 18 May 2013, 07:58

# Is OG Quant question answer wrong?

Author Message
TAGS:
Manager
Joined: 17 Jan 2010
Posts: 153
Concentration: General Management, Strategy
GPA: 3.78
WE: Engineering (Manufacturing)
Followers: 1

Kudos [?]: 24 [0], given: 11

00:00

Question Stats:

25% (01:09) correct 75% (00:41) wrong based on 0 sessions
This is the question from GMAT Quant Review:

If x is a positive integer , is \sqrt{x} an integer?

(1) \sqrt{4x} is an integer.
(2) \sqrt{3x} is not an integer.

My logic to solve this question:

\sqrt{4x}=2*\sqrt{x}, so \sqrt{x} can either be integer or not an integer (for example \sqrt{x}=2.5) and the 2*\sqrt{x} is still an integer. So Statement 1 is insufficient.

\sqrt{3x}= \sqrt{3}*\sqrt{x}. As \sqrt{3} is not an integer, the \sqrt{x} can be either integer or non integer and the \sqrt{3}*\sqrt{x} will still be not integer. So Statement 2 is insufficient.

S1 and S2 together is still insufficient as \sqrt{x}=2 and \sqrt{x}=2.5 both satisfy statements requirement.

So I choose E as an answer.

Is there a flaw in my reasoning? OG Quant review answer to this question is different from E.
 Kaplan GMAT Prep Discount Codes Knewton GMAT Discount Codes Veritas Prep GMAT Discount Codes
Senior Manager
Joined: 22 Dec 2009
Posts: 368
Followers: 9

Kudos [?]: 136 [0], given: 47

Re: Is OG Quant question answer wrong? [#permalink]  20 Feb 2010, 15:14
alexBLR wrote:
This is the question from GMAT Quant Review:

If x is a positive integer , is \sqrt{x} an integer?

1) \sqrt{4x} is an integer.
2) \sqrt{3x} is not an integer.

My logic to solve this question:

\sqrt{4x}=2*\sqrt{x}, so \sqrt{x} can either be integer or not an integer (for example \sqrt{x}=2.5) and the 2*\sqrt{x} is still an integer. So Statement 1 is insufficient.

\sqrt{3x}= \sqrt{3}*\sqrt{x}. As \sqrt{3} is not an integer, the \sqrt{x} can be either integer or non integer and the \sqrt{3}*\sqrt{x} will still be not integer. So Statement 2 is insufficient.

S1 and S2 together is still insufficient as \sqrt{x}=2 and \sqrt{x}=2.5 both satisfy statements requirement.

So I choose E as an answer.

Is there a flaw in my reasoning? OG Quant review answer to this question is different from E.

IMO D...

Ques: if x is a positive integer, is \sqrt{x} an integer?

S1: \sqrt{4x} is an integer

--> 2* \sqrt{x} is an integer --> \sqrt{x} has to be an integer.. as x is a positive integer and hence cannot be a fraction. Therefore SUFF

S2: \sqrt{3x} is an integer
--> \sqrt{3}*\sqrt{x} --> \sqrt{x} is not an integer as same could be a of a form of a\sqrt{3} where 'a' is a positive integer. Therefore SUFF
_________________

Cheers!
JT...........
If u like my post..... payback in Kudos!!

|For CR refer Powerscore CR Bible|For SC refer Manhattan SC Guide|

~~Better Burn Out... Than Fade Away~~

GMAT Club team member
Joined: 02 Sep 2009
Posts: 11506
Followers: 1791

Kudos [?]: 9517 [3] , given: 826

Re: Is OG Quant question answer wrong? [#permalink]  20 Feb 2010, 15:57
3
KUDOS
jeeteshsingh wrote:
alexBLR wrote:
This is the question from GMAT Quant Review:

If x is a positive integer , is \sqrt{x} an integer?

1) \sqrt{4x} is an integer.
2) \sqrt{3x} is not an integer.

My logic to solve this question:

\sqrt{4x}=2*\sqrt{x}, so \sqrt{x} can either be integer or not an integer (for example \sqrt{x}=2.5) and the 2*\sqrt{x} is still an integer. So Statement 1 is insufficient.

\sqrt{3x}= \sqrt{3}*\sqrt{x}. As \sqrt{3} is not an integer, the \sqrt{x} can be either integer or non integer and the \sqrt{3}*\sqrt{x} will still be not integer. So Statement 2 is insufficient.

S1 and S2 together is still insufficient as \sqrt{x}=2 and \sqrt{x}=2.5 both satisfy statements requirement.

So I choose E as an answer.

Is there a flaw in my reasoning? OG Quant review answer to this question is different from E.

IMO D...

Ques: if x is a positive integer, is \sqrt{x} an integer?

S1: \sqrt{4x} is an integer

--> 2* \sqrt{x} is an integer --> \sqrt{x} has to be an integer.. as x is a positive integer and hence cannot be a fraction. Therefore SUFF

S2: \sqrt{3x} is an integer
--> \sqrt{3}*\sqrt{x} --> \sqrt{x} is not an integer as same could be a of a form of a\sqrt{3} where 'a' is a positive integer. Therefore SUFF

As given that x is a positive integer then \sqrt{x} is either an integer itself or an irrational number.

(1) \sqrt{4x} is an integer --> 2\sqrt{x}=integer --> 2\sqrt{x} to be an integer \sqrt{x} must be an integer or integer/2, but as x is an integer, then \sqrt{x} can not be integer/2, hence \sqrt{x} is an integer. Sufficient.

(2) \sqrt{3x} is not an integer --> if x=9, condition \sqrt{3x}=\sqrt{27} is not an integer satisfied and \sqrt{x}=3 IS an integer, BUT if x=2, condition \sqrt{3x}=\sqrt{6} is not an integer satisfied and \sqrt{x}=\sqrt{2} IS NOT an integer. Two different answers. Not sufficient.

jeeteshsingh, you should have spotted that there was something wrong with your solution as in DS two statements can not give you TWO DIFFERENT answers to the question (as you've got).

Hope it helps.
_________________
Senior Manager
Joined: 22 Dec 2009
Posts: 368
Followers: 9

Kudos [?]: 136 [0], given: 47

Re: Is OG Quant question answer wrong? [#permalink]  20 Feb 2010, 16:13
Bunuel wrote:
jeeteshsingh, you should have spotted that there was something wrong with your solution as in DS two statements can not give you TWO DIFFERENT answers to the question (as you've got).

Hope it helps.

My Bad.... overlooked it... Infact today I was telling this to someone over the forum that both the statements in DS would always be in sync..

Thanks Bunuel... for pointing this out.
_________________

Cheers!
JT...........
If u like my post..... payback in Kudos!!

|For CR refer Powerscore CR Bible|For SC refer Manhattan SC Guide|

~~Better Burn Out... Than Fade Away~~

Manager
Joined: 17 Jan 2010
Posts: 153
Concentration: General Management, Strategy
GPA: 3.78
WE: Engineering (Manufacturing)
Followers: 1

Kudos [?]: 24 [0], given: 11

Re: Is OG Quant question answer wrong? [#permalink]  20 Feb 2010, 16:42
When I assumed the case \sqrt{x}=2.5 I did not take into the account that x will not be an integer in this case(x=6.25). Thanks Bunuel
Manager
Joined: 26 Feb 2011
Posts: 50
Followers: 1

Kudos [?]: 1 [0], given: 1

Integers [#permalink]  28 Feb 2011, 12:43
If x is positive integer, is \sqrt{x} an integer?
1) \sqrt{4x} is an integer
2) \sqrt{3x} is not an integer
GMAT Club team member
Joined: 02 Sep 2009
Posts: 11506
Followers: 1791

Kudos [?]: 9517 [0], given: 826

Re: Integers [#permalink]  28 Feb 2011, 12:56
Re: Integers   [#permalink] 28 Feb 2011, 12:56
Similar topics Replies Last post
Similar
Topics:
Answers that did not make sense in OG Quant 3 25 Sep 2006, 09:36
Wrong Answer in Official Guide (Quant Review-I #117) 4 10 Apr 2010, 17:33
Every 3rd question I answered is wrong 1 27 Apr 2011, 22:39
1 coordenates question - should be easy, is the answer wrong? 2 22 Jun 2011, 07:47
Quant Question...Answer Pls 2 06 Nov 2011, 10:03
Display posts from previous: Sort by