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

It is currently 24 Apr 2014, 19:14

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If x is an integer, is x|x| < 2x? (1) x < 0 (2) x =

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
SVP
SVP
User avatar
Joined: 11 Mar 2008
Posts: 1634
Location: Southern California
Schools: Chicago (dinged), Tuck (November), Columbia (RD)
Followers: 7

Kudos [?]: 170 [0], given: 0

GMAT Tests User
If x is an integer, is x|x| < 2x? (1) x < 0 (2) x = [#permalink] New post 25 Jun 2008, 09:07
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
If x is an integer, is x|x| < 2x?

(1) x < 0
(2) x = -10

The OA is D. Statement 2 is obviously sufficient. I don't understand how statement 1 is sufficient?

Take the example of x = -2.

-2(2) = 2(-2) - therefore x|x| = 2x

Take the example of x = -3.

-3(3) < 2(-3) - therefore x|x| < 2x
_________________

Check out the new Career Forum
http://gmatclub.com/forum/133

Manager
Manager
User avatar
Joined: 11 Apr 2008
Posts: 130
Location: Chicago
Followers: 1

Kudos [?]: 29 [0], given: 0

Re: OG DS 128 [#permalink] New post 25 Jun 2008, 09:36
terp06 wrote:
If x is an integer, is x|x| < 2x?

(1) x < 0
(2) x = -10

The OA is D. Statement 2 is obviously sufficient. I don't understand how statement 1 is sufficient?

Take the example of x = -2.

-2(2) = 2(-2) - therefore x|x| = 2x

Take the example of x = -3.

-3(3) < 2(-3) - therefore x|x| < 2x


You did all the work :x

Yes, answer is D
_________________

Factorials were someone's attempt to make math look exciting!!!

SVP
SVP
User avatar
Joined: 11 Mar 2008
Posts: 1634
Location: Southern California
Schools: Chicago (dinged), Tuck (November), Columbia (RD)
Followers: 7

Kudos [?]: 170 [0], given: 0

GMAT Tests User
Re: OG DS 128 [#permalink] New post 25 Jun 2008, 09:42
brokerbevo wrote:
terp06 wrote:
If x is an integer, is x|x| < 2x?

(1) x < 0
(2) x = -10

The OA is D. Statement 2 is obviously sufficient. I don't understand how statement 1 is sufficient?

Take the example of x = -2.

-2(2) = 2(-2) - therefore x|x| = 2x

Take the example of x = -3.

-3(3) < 2(-3) - therefore x|x| < 2x


You did all the work :x

Yes, answer is D


With the work I did above, I thought the answer would be B? I found 2 negative integers for statement 1, 1 which satisfies the condition and one which does not, meaning that statement 1 should be insufficient?
_________________

Check out the new Career Forum
http://gmatclub.com/forum/133

Director
Director
Joined: 01 Jan 2008
Posts: 629
Followers: 3

Kudos [?]: 124 [0], given: 1

GMAT Tests User
Re: OG DS 128 [#permalink] New post 25 Jun 2008, 09:50
terp06 wrote:
If x is an integer, is x|x| < 2x?

(1) x < 0
(2) x = -10

The OA is D. Statement 2 is obviously sufficient. I don't understand how statement 1 is sufficient?

Take the example of x = -2.

-2(2) = 2(-2) - therefore x|x| = 2x

Take the example of x = -3.

-3(3) < 2(-3) - therefore x|x| < 2x


As you said statement 1 is not sufficient.

x = -1 -> x*abs(x) = -1 > 2*(-1)
x = -3 -> x*abs(x) = -9 < -6 = 2*(-3)

D is incorrect, the answer has to be B.
Manager
Manager
User avatar
Joined: 11 Apr 2008
Posts: 130
Location: Chicago
Followers: 1

Kudos [?]: 29 [0], given: 0

Re: OG DS 128 [#permalink] New post 25 Jun 2008, 10:02
terp06 wrote:
brokerbevo wrote:
terp06 wrote:
If x is an integer, is x|x| < 2x?

(1) x < 0
(2) x = -10

The OA is D. Statement 2 is obviously sufficient. I don't understand how statement 1 is sufficient?

Take the example of x = -2.

-2(2) = 2(-2) - therefore x|x| = 2x

Take the example of x = -3.

-3(3) < 2(-3) - therefore x|x| < 2x


You did all the work :x

Yes, answer is D


With the work I did above, I thought the answer would be B? I found 2 negative integers for statement 1, 1 which satisfies the condition and one which does not, meaning that statement 1 should be insufficient?


Yes, maybe I should read your entire post. Sorry about that. Yes, the answer should be B Where did you find this problem?
_________________

Factorials were someone's attempt to make math look exciting!!!

SVP
SVP
User avatar
Joined: 11 Mar 2008
Posts: 1634
Location: Southern California
Schools: Chicago (dinged), Tuck (November), Columbia (RD)
Followers: 7

Kudos [?]: 170 [0], given: 0

GMAT Tests User
Re: OG DS 128 [#permalink] New post 25 Jun 2008, 10:03
This problem is in the OG11 and the OA is D.
_________________

Check out the new Career Forum
http://gmatclub.com/forum/133

Manager
Manager
User avatar
Joined: 11 Apr 2008
Posts: 130
Location: Chicago
Followers: 1

Kudos [?]: 29 [0], given: 0

Re: OG DS 128 [#permalink] New post 25 Jun 2008, 10:09
terp06 wrote:
This problem is in the OG11 and the OA is D.


Hmm. What is the explanation in the back of the book for how they arrived at D? Because even moreover, if you try -1 the inequality is > and if you try -3 the inequality is < and if you try -2, it is an equality --> Its all over the charts!! :shock:
_________________

Factorials were someone's attempt to make math look exciting!!!

Intern
Intern
Joined: 30 Jul 2007
Posts: 35
Followers: 0

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

Re: OG DS 128 [#permalink] New post 25 Jun 2008, 10:46
terp06 wrote:
If x is an integer, is x|x| < 2x?

(1) x < 0
(2) x = -10

The OA is D. Statement 2 is obviously sufficient. I don't understand how statement 1 is sufficient?


You wrote the question incorrectly. It makes a huge difference.

The question is:

If x is an integer, is x |x| < 2^x?

(1) x < 0
(2) x = -10

Statement one, plug in (-1,-2)

-1 > 1/2 yes
-4 > 1/4 yes

Sufficient

Statement 2

-20 < -1/2^10

Sufficient

Therefore, answer is D.

Last edited by 2010mba on 25 Jun 2008, 11:02, edited 1 time in total.
SVP
SVP
User avatar
Joined: 11 Mar 2008
Posts: 1634
Location: Southern California
Schools: Chicago (dinged), Tuck (November), Columbia (RD)
Followers: 7

Kudos [?]: 170 [0], given: 0

GMAT Tests User
Re: OG DS 128 [#permalink] New post 25 Jun 2008, 11:33
2010mba wrote:
terp06 wrote:
If x is an integer, is x|x| < 2x?

(1) x < 0
(2) x = -10

The OA is D. Statement 2 is obviously sufficient. I don't understand how statement 1 is sufficient?


You wrote the question incorrectly. It makes a huge difference.

The question is:

If x is an integer, is x |x| < 2^x?

(1) x < 0
(2) x = -10

Statement one, plug in (-1,-2)

-1 > 1/2 yes
-4 > 1/4 yes

Sufficient

Statement 2

-20 < -1/2^10

Sufficient

Therefore, answer is D.


In the book, it is written as 2x.
_________________

Check out the new Career Forum
http://gmatclub.com/forum/133

Intern
Intern
Joined: 30 Jul 2007
Posts: 35
Followers: 0

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

Re: OG DS 128 [#permalink] New post 26 Jun 2008, 09:21
terp06 wrote:
In the book, it is written as 2x.


The x is small, and half way up the 2, meaning it is an exponent. I hope that helps. If it were 2x, then the x would be on same line as the 2.
Current Student
User avatar
Joined: 12 Jun 2008
Posts: 288
Schools: INSEAD Class of July '10
Followers: 5

Kudos [?]: 33 [0], given: 0

GMAT Tests User
Re: OG DS 128 [#permalink] New post 26 Jun 2008, 10:08
2010mba wrote:
The question is:

If x is an integer, is x |x| < 2^x?

(1) x < 0
(2) x = -10

Statement one, plug in (-1,-2)

-1 > 1/2 yes
-4 > 1/4 yes

Sufficient

Is this a proof (1) is sufficient ?? You just test it for 2 values (why -1 and -2 by the way ?) and therefore it is sufficient ? Are you sure it works for x=-1/8 ? ;)

I would say something like: if x<0, then x |x| <0

And since 2^x is positive, then we have x |x| < 2^x (this is no longer that plugging numbers ;))
GMAT Instructor
Joined: 24 Jun 2008
Posts: 967
Location: Toronto
Followers: 237

Kudos [?]: 578 [0], given: 3

GMAT Tests User
Re: OG DS 128 [#permalink] New post 27 Jun 2008, 13:47
2010mba wrote:
terp06 wrote:
In the book, it is written as 2x.


The x is small, and half way up the 2, meaning it is an exponent. I hope that helps. If it were 2x, then the x would be on same line as the 2.


My understanding is that this is printed incorrectly in earlier printings of the Guide, and was later corrected. In some books, it is actually printed as 2x, and not as 2^x, in the question (though not in the solution section of the book).
_________________

Nov 2011: After years of development, I am now making my advanced Quant books and high-level problem sets available for sale. Contact me at ianstewartgmat at gmail.com for details.

Private GMAT Tutor based in Toronto

Current Student
User avatar
Joined: 12 Jun 2008
Posts: 288
Schools: INSEAD Class of July '10
Followers: 5

Kudos [?]: 33 [0], given: 0

GMAT Tests User
Re: OG DS 128 [#permalink] New post 29 Jun 2008, 13:42
2010mba wrote:
It says x is an integer.

Yeah, okay...

So (if you prefer): did you try x= -4679? x= -27? :roll:
Intern
Intern
Joined: 18 Feb 2008
Posts: 31
Followers: 0

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

Re: OG DS 128 [#permalink] New post 01 Jul 2008, 02:24
Oski wrote:
2010mba wrote:
It says x is an integer.

Yeah, okay...

So (if you prefer): did you try x= -4679? x= -27? :roll:


I think 2^-27 will still be a positive value !!
Current Student
User avatar
Joined: 12 Jun 2008
Posts: 288
Schools: INSEAD Class of July '10
Followers: 5

Kudos [?]: 33 [0], given: 0

GMAT Tests User
Re: OG DS 128 [#permalink] New post 01 Jul 2008, 02:36
saurabhkowley18 wrote:
I think 2^-27 will still be a positive value !!

I know.

But the reason for that IS NOT that it is the case for x=-1 and x=-2
Re: OG DS 128   [#permalink] 01 Jul 2008, 02:36
    Similar topics Author Replies Last post
Similar
Topics:
New posts Is 1+x+x^2+x^3+x^4 > 1/(1-x) ? 1). x > 0 2). x < 1 TeHCM 6 04 Feb 2006, 22:13
New posts Is 1+x+x^2+x^3+x^4 > 1/(1-x) ? (1) x > 0 (2) x < 1 laxieqv 6 25 Feb 2006, 21:36
New posts Is 1+x+x^2+x^3+x^4 > 1/ (1-x)? (1) x > 0 (2) x < 1 vivek123 1 04 Mar 2006, 21:22
New posts 1 Experts publish their posts in the topic If x is an integer, is x|x| < 2^x? rohitgoel15 4 22 Mar 2010, 20:59
New posts 2 Experts publish their posts in the topic If x is an integer, is x|x| < 2^x? cucrose 8 17 Jan 2007, 15:27
Display posts from previous: Sort by

If x is an integer, is x|x| < 2x? (1) x < 0 (2) x =

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.