Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 30 May 2017, 00:02

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# If ab≠0 and points (-a,b) and (-b,a) are in the same

Author Message
TAGS:

### Hide Tags

Director
Joined: 04 Jan 2008
Posts: 898
Followers: 72

Kudos [?]: 623 [0], given: 17

Re: GMAT Prep - DS 6 [#permalink]

### Show Tags

01 Sep 2009, 03:28
Always post in .jpg so that screenshot will be seen from distance(no need to download)

this is a good Q

It must be in II or IVth quadrants
a and b both Positive or both negative [EDITED]

now we need both the conditions

(2) will give x--Positive(becoz ax>0 and a is +ve)
(1) will give y-Positive(becoz xy>0 and x is +ve)
Attachments

DS 6.JPG [ 39.83 KiB | Viewed 966 times ]

_________________

http://gmatclub.com/forum/math-polygons-87336.html
http://gmatclub.com/forum/competition-for-the-best-gmat-error-log-template-86232.html

Last edited by nitya34 on 01 Sep 2009, 08:02, edited 1 time in total.
Current Student
Joined: 13 Jul 2009
Posts: 145
Location: Barcelona
Schools: SSE
Followers: 17

Kudos [?]: 379 [1] , given: 22

Re: GMAT Prep - DS 6 [#permalink]

### Show Tags

01 Sep 2009, 04:21
1
KUDOS
I don't understand your explanation, nitya34.
Why a must be positive?

IMO from the first part of the question we can extract that a & b must be of the same sign, either positive or negative:

$$a=2, b=3$$
$$(-2, 3), (-3, 2)$$ -> same quadrant

$$a=-2, b=-3$$
$$(2, -3), (3, -2)$$ -> same quadrant

$$a=-2, b=3$$
$$(2, 3), (-3, -2)$$ -> different quadrant

From (1) we know that x & y must be of the same sign too, but we don't know whether positive or negative and therefore it is insufficient.
From (2) we know that a & x must be of the same sign but we don't know anything about Y, therefore it is insufficient.
From (1) & (2) we know that a,b,x,y must be of the same sign and therefore are in the same quadrant = sufficient.

That's they way I tackled it.
_________________

Performance: Gmat | Toefl
Contributions: The Idioms Test | All Geometry Formulas | Friendly Error Log | GMAT Analytics
MSc in Management: All you need to know | Student Lifestyle | Class Profiles

Manager
Joined: 10 Jul 2009
Posts: 165
Followers: 2

Kudos [?]: 106 [0], given: 8

Re: GMAT Prep - DS 6 [#permalink]

### Show Tags

01 Sep 2009, 08:24
Agree with Saruba, answer is C
Senior Manager
Status: Time to step up the tempo
Joined: 24 Jun 2010
Posts: 408
Location: Milky way
Schools: ISB, Tepper - CMU, Chicago Booth, LSB
Followers: 8

Kudos [?]: 211 [0], given: 50

Re: DS question : need help [#permalink]

### Show Tags

07 Oct 2010, 18:12
satishreddy wrote:
157) If ab ≠ 0 and (-a, b) and (-b, a) are in the same quadrant, is (-x, y) in this quadrant?
a. xy > 0
b. ax > 0

OA:

Given that (-a,b) and (-b,a) are in the same quadrant. Hence we can deduce that the points are either in the I or III quadrant.

We need to determine whether (-x,y) also belongs to either I or III quadrant.

Statement A: xy>0. With this, we can deduce that either both x and y is +ve or both -ve.

However we cannot tie this information with the two given points (-a,b) and (-b,a). Insufficient.

Statement B: ax>0. With this again, we can deduce that either both a and x is +ve or both -ve. But we do not have sufficient information about y hence we cannot make out if (-x,y) is in the I or III quadrant. Insufficient.

With both the statement put together, we know that the sign of a and x is the same and the sign of x and y is the same. Hence we can deduce that the sign of x and y is the same. If the sign of x and y is the same then the point (-x,y) should also be in the I or III quadrant.

_________________

Support GMAT Club by putting a GMAT Club badge on your blog

CEO
Status: Nothing comes easy: neither do I want.
Joined: 12 Oct 2009
Posts: 2786
Location: Malaysia
Concentration: Technology, Entrepreneurship
Schools: ISB '15 (M)
GMAT 1: 670 Q49 V31
GMAT 2: 710 Q50 V35
Followers: 238

Kudos [?]: 1731 [1] , given: 235

Re: DS question : need help [#permalink]

### Show Tags

07 Oct 2010, 18:36
1
KUDOS
ezhilkumarank wrote:
satishreddy wrote:
157) If ab ≠ 0 and (-a, b) and (-b, a) are in the same quadrant, is (-x, y) in this quadrant?
a. xy > 0
b. ax > 0

OA:

Given that (-a,b) and (-b,a) are in the same quadrant. Hence we can deduce that the points are either in the I or III quadrant.

We need to determine whether (-x,y) also belongs to either I or III quadrant.

Statement A: xy>0. With this, we can deduce that either both x and y is +ve or both -ve.

However we cannot tie this information with the two given points (-a,b) and (-b,a). Insufficient.

Statement B: ax>0. With this again, we can deduce that either both a and x is +ve or both -ve. But we do not have sufficient information about y hence we cannot make out if (-x,y) is in the I or III quadrant. Insufficient.

With both the statement put together, we know that the sign of a and x is the same and the sign of x and y is the same. Hence we can deduce that the sign of x and y is the same. If the sign of x and y is the same then the point (-x,y) should also be in the I or III quadrant.

How can you deduce - "Hence we can deduce that the points are either in the I or III quadrant." ???
Also whatever you have proved using statement 1 and 2 can be proved by the statement 1 alone.

take a = 2 and b = 1 => -a,b = -2,1 and -b,a = -1,2 -------> both lies in 2nd quadrant. Also if you interchange the signs it can be proved that they lie in the 4th quadrant.

=> either both a and b are +ve or -ve i.e. both should have the same sign.

If it is not true, suppose a =1 and b = -2 => -a,b = -1,-2 and -b,a = 2,1 => do they lie in same quadrant? NO

Statement 1. xy>0 => either both are -ve or both are +ve => either (-x, y) is in 2nd or 4th quadrant. Hence not sufficient.

Statement 2. ax>0 => a and x have same sign. Since we do not know anything of b and y we can not predict. No sufficient.

Statement 1 and 2 taken together: x and y have same sign. a and x have same sign => a,b,x,y all have the same sign.
=> if a and b have -ve sign then x and y also have -ve sign and vice versa.
=> the required point lies in the quadrant in which the given two lie.

Hence C

Note: If we prove (-x, y) either lie in 2 or 4 quadrant, then it is wrong. it is possible that the two points lie in 2nd and the given point (-x, y) lies in the 4th.

I must say - very good question. What is the source?
_________________

Fight for your dreams :For all those who fear from Verbal- lets give it a fight

Money Saved is the Money Earned

Jo Bole So Nihaal , Sat Shri Akaal

GMAT Club Premium Membership - big benefits and savings

Gmat test review :
http://gmatclub.com/forum/670-to-710-a-long-journey-without-destination-still-happy-141642.html

Intern
Joined: 14 Aug 2010
Posts: 33
Followers: 0

Kudos [?]: 29 [0], given: 3

Re: DS question : need help [#permalink]

### Show Tags

07 Oct 2010, 18:52
"With both the statement put together, we know that the sign of a and x is the same and the sign of x and y is the same. Hence we can deduce that the sign of x and y is the same. If the sign of x and y is the same then the point (-x,y) should also be in the I or III quadrant."

I dont understand your reasoning. Just from (1) you know sign of x & y is the same.
Why do you need to deduce from (1) & (2) ?

Given : (-a,b) & (-b,a) are in the same quadrant ==> a & b should have same sign.
from (i) x,y have same sign
from (ii) a,x have same sign
Together from (i) , (ii) and given information
Sign of a=b=x=y . Hence (-x,y) will be in the same quadrant as (-a,b) & (-b,a)
Intern
Joined: 25 Sep 2010
Posts: 20
Followers: 0

Kudos [?]: 39 [0], given: 7

Re: DS question : need help [#permalink]

### Show Tags

07 Oct 2010, 19:52
thank you so, so, much,,,i appreciate
Retired Moderator
Joined: 02 Sep 2010
Posts: 803
Location: London
Followers: 111

Kudos [?]: 1024 [0], given: 25

Re: DS question : need help [#permalink]

### Show Tags

08 Oct 2010, 00:31
Merging similar topics
_________________
Senior Manager
Status: Time to step up the tempo
Joined: 24 Jun 2010
Posts: 408
Location: Milky way
Schools: ISB, Tepper - CMU, Chicago Booth, LSB
Followers: 8

Kudos [?]: 211 [0], given: 50

Re: DS question : need help [#permalink]

### Show Tags

08 Oct 2010, 09:21
gurpreetsingh wrote:
ezhilkumarank wrote:
satishreddy wrote:
157) If ab ≠ 0 and (-a, b) and (-b, a) are in the same quadrant, is (-x, y) in this quadrant?
a. xy > 0
b. ax > 0

OA:

Given that (-a,b) and (-b,a) are in the same quadrant. Hence we can deduce that the points are either in the I or III quadrant.

We need to determine whether (-x,y) also belongs to either I or III quadrant.

Statement A: xy>0. With this, we can deduce that either both x and y is +ve or both -ve.

However we cannot tie this information with the two given points (-a,b) and (-b,a). Insufficient.

Statement B: ax>0. With this again, we can deduce that either both a and x is +ve or both -ve. But we do not have sufficient information about y hence we cannot make out if (-x,y) is in the I or III quadrant. Insufficient.

With both the statement put together, we know that the sign of a and x is the same and the sign of x and y is the same. Hence we can deduce that the sign of x and y is the same. If the sign of x and y is the same then the point (-x,y) should also be in the I or III quadrant.

How can you deduce - "Hence we can deduce that the points are either in the I or III quadrant." ???
Also whatever you have proved using statement 1 and 2 can be proved by the statement 1 alone.

take a = 2 and b = 1 => -a,b = -2,1 and -b,a = -1,2 -------> both lies in 2nd quadrant. Also if you interchange the signs it can be proved that they lie in the 4th quadrant.

=> either both a and b are +ve or -ve i.e. both should have the same sign.

If it is not true, suppose a =1 and b = -2 => -a,b = -1,-2 and -b,a = 2,1 => do they lie in same quadrant? NO

Statement 1. xy>0 => either both are -ve or both are +ve => either (-x, y) is in 2nd or 4th quadrant. Hence not sufficient.

Statement 2. ax>0 => a and x have same sign. Since we do not know anything of b and y we can not predict. No sufficient.

Statement 1 and 2 taken together: x and y have same sign. a and x have same sign => a,b,x,y all have the same sign.
=> if a and b have -ve sign then x and y also have -ve sign and vice versa.
=> the required point lies in the quadrant in which the given two lie.

Hence C

Note: If we prove (-x, y) either lie in 2 or 4 quadrant, then it is wrong. it is possible that the two points lie in 2nd and the given point (-x, y) lies in the 4th.

I must say - very good question. What is the source?

Yes Gurpreet, you are correct. I madly rushed through the problem after incorrectly assuming that (-a,b) and (-b,a) are in the same quadrant. Thanks for pointing it out and also for the solution. +1 to you.
_________________

Support GMAT Club by putting a GMAT Club badge on your blog

Retired Moderator
Status: 2000 posts! I don't know whether I should feel great or sad about it! LOL
Joined: 04 Oct 2009
Posts: 1669
Location: Peru
Schools: Harvard, Stanford, Wharton, MIT & HKS (Government)
WE 1: Economic research
WE 2: Banking
WE 3: Government: Foreign Trade and SMEs
Followers: 103

Kudos [?]: 995 [0], given: 109

### Show Tags

26 Oct 2010, 17:30
If a*b is not zero and points (-a, b) and (-b, a) are in the same quadrant of the xy-plane, is point (-x, y) in this same quadrant?

(1) $$xy > 0$$
(2) $$ax > 0$$

Enjoy.
_________________

"Life’s battle doesn’t always go to stronger or faster men; but sooner or later the man who wins is the one who thinks he can."

My Integrated Reasoning Logbook / Diary: http://gmatclub.com/forum/my-ir-logbook-diary-133264.html

GMAT Club Premium Membership - big benefits and savings

Intern
Joined: 14 Sep 2010
Posts: 22
Followers: 1

Kudos [?]: 52 [0], given: 0

### Show Tags

26 Jan 2011, 08:28
If ab is not equal to 0 , and points (-a,b) and (-b,a) are in the same quadrant of the xy – plane , is point (-x,y) in this same quadrant?
1) xy > 0
2) ax > 0
Math Expert
Joined: 02 Sep 2009
Posts: 39066
Followers: 7759

Kudos [?]: 106596 [0], given: 11630

Re: GMAT PREP Coordinate Geometry [#permalink]

### Show Tags

26 Jan 2011, 08:32
Merging similar topics.
_________________
Intern
Joined: 19 Jul 2011
Posts: 24
Followers: 0

Kudos [?]: 5 [0], given: 2

Data Sufficiency Question GMAT Prep [#permalink]

### Show Tags

15 Aug 2011, 06:42
Hi everyone..would appreciate if you could solution to the question below...thanks in advance.

If axb (a times b) is different than zero and points (-a, b) and (-b,a) are in the same quadrant of the xy-plane is point (-x,y) in this same quadrant?

(1) xy>0
(2) ax>0
Manager
Status: Quant 50+?
Joined: 02 Feb 2011
Posts: 107
Concentration: Strategy, Finance
Schools: Tuck '16, Darden '16
Followers: 1

Kudos [?]: 28 [0], given: 22

Re: Data Sufficiency Question GMAT Prep [#permalink]

### Show Tags

15 Aug 2011, 07:26
Question tells us that A and B have the same sign.
(1) Not sufficient because xy could both be negative and ab could both be positive or vice-versa
(2) NS because ax having the same sign does not mean by do as well
Together sufficient because we know xy have the same sign, and that sign is the same as a
Intern
Joined: 19 Jul 2011
Posts: 24
Followers: 0

Kudos [?]: 5 [0], given: 2

### Show Tags

15 Aug 2011, 12:20
one question..Stem says, both points are in 2nd or 4th quad  which is assuming +, + or -,- for a and b, since a times b is different than zero..how come we dont evaluate +,- and -,+ options for a and b? thanks

Go to page   Previous    1   2   3   4   5   6   7   [ 135 posts ]

Similar topics Replies Last post
Similar
Topics:
3 If ab≠0, √((5a+6b)/(a+3b))=? 2 03 Jul 2016, 05:47
5 If a*b≠0, and (x−a)(x+b)=0, is b=a? 4 09 Jul 2016, 13:20
78 If ab≠0 and points (-a, b) and (-b, a) are in the same quadr 20 01 Oct 2016, 10:37
3 If ab≠0 and points (-a,b) and (-b,a) are in the same quadran 4 13 Oct 2013, 15:53
11 If ab <> 0 and points (-a,b) and (-b,a) are in the same 12 22 Apr 2012, 19:57
Display posts from previous: Sort by