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## GMAT DS GMATPrep

This topic has 11 member replies
bicilotti Newbie | Next Rank: 10 Posts
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#### GMAT DS GMATPrep

Tue Apr 10, 2007 4:47 am
Two points (-a,b) (-b,a) are in the same quadrant of the xy plane. Is the point (-x,y) in the same plane?

(i) xy>0
(ii) ax>0

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guynoor Senior | Next Rank: 100 Posts
Joined
10 Feb 2007
Posted:
59 messages
1
Tue Apr 10, 2007 5:54 am
gabriel wrote:
bicilotti wrote:
Two points (-a,b) (-b,a) are in the same quadrant of the xy plane. Is the point (-x,y) in the same plane?

(i) xy>0
(ii) ax>0

given that (-a ,b) and (-b,a) are in the same quadrant .. that means both a and b have tha same sign .. that is they are eoither both positive ( in which case the 2 points are both are in the second quadrant ) or they are both negative ( in which case the 2 points are in the 4th quadrant )..

now the first statement says that xy>0.. so x and y have the same sign (they are either positve or negative ) .. that means (-x,y) is either in the 2nd or the 4th quadrant .. but since we dont know what is the positoin of (-a,b) and(-b,a) .. we dont have a defnite answer .. so not sufficient..

the second statement says that ax>0 .. again we have a,x and b (bcoz a and b have the same sign ) have the same sign ..but since we dont know the sign of y the statemant is insufficient..

now combine the 2 statements .. we have from the first statemnt x, y have the same sign ... from the 2nd statement we have a,x have the same sign .. so we get a,b,x,y have the same sign .. so now we can conclusively say that all the three points lie in the same quadrant ... if they are positive they will lie in the 3rd quadrant .. if they are negative the points will lie in the 4 th quadrant .. so the answer is C
Doesn't it matter that they already provide you with -ve signs for both a and b as x and y coordinates for the 2 points. If thats the case then we know for sure that the 2 point would be in the 2nd Quad...If there can be the possibility if being in 2 Quadrants why even give the 2 -ve signs, why didn't they just give (a,b) and (b,a)???

bicilotti Newbie | Next Rank: 10 Posts
Joined
10 Apr 2007
Posted:
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Tue Apr 10, 2007 5:32 am
thank you sooooooooooo much for the clear explanation!

guynoor Senior | Next Rank: 100 Posts
Joined
10 Feb 2007
Posted:
59 messages
1
Tue Apr 10, 2007 5:54 am
gabriel wrote:
bicilotti wrote:
Two points (-a,b) (-b,a) are in the same quadrant of the xy plane. Is the point (-x,y) in the same plane?

(i) xy>0
(ii) ax>0

given that (-a ,b) and (-b,a) are in the same quadrant .. that means both a and b have tha same sign .. that is they are eoither both positive ( in which case the 2 points are both are in the second quadrant ) or they are both negative ( in which case the 2 points are in the 4th quadrant )..

now the first statement says that xy>0.. so x and y have the same sign (they are either positve or negative ) .. that means (-x,y) is either in the 2nd or the 4th quadrant .. but since we dont know what is the positoin of (-a,b) and(-b,a) .. we dont have a defnite answer .. so not sufficient..

the second statement says that ax>0 .. again we have a,x and b (bcoz a and b have the same sign ) have the same sign ..but since we dont know the sign of y the statemant is insufficient..

now combine the 2 statements .. we have from the first statemnt x, y have the same sign ... from the 2nd statement we have a,x have the same sign .. so we get a,b,x,y have the same sign .. so now we can conclusively say that all the three points lie in the same quadrant ... if they are positive they will lie in the 3rd quadrant .. if they are negative the points will lie in the 4 th quadrant .. so the answer is C
Doesn't it matter that they already provide you with -ve signs for both a and b as x and y coordinates for the 2 points. If thats the case then we know for sure that the 2 point would be in the 2nd Quad...If there can be the possibility if being in 2 Quadrants why even give the 2 -ve signs, why didn't they just give (a,b) and (b,a)???

bicilotti Newbie | Next Rank: 10 Posts
Joined
10 Apr 2007
Posted:
3 messages
Tue Apr 10, 2007 5:32 am
thank you sooooooooooo much for the clear explanation!

Cybermusings Legendary Member
Joined
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Thu Apr 12, 2007 7:38 am
thank you gabriel...co-ordinate geometry sometimes gets crazy!

RAGS Senior | Next Rank: 100 Posts
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Thu Apr 12, 2007 7:02 am
R they asking if the point lies in same plane
There is only on eplane ie X-Y plane where else would the point lie???????????

gabriel Legendary Member
Joined
20 Dec 2006
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Tue Apr 10, 2007 10:20 pm
guynoor wrote:
gabriel wrote:
bicilotti wrote:
Two points (-a,b) (-b,a) are in the same quadrant of the xy plane. Is the point (-x,y) in the same plane?

(i) xy>0
(ii) ax>0

given that (-a ,b) and (-b,a) are in the same quadrant .. that means both a and b have tha same sign .. that is they are eoither both positive ( in which case the 2 points are both are in the second quadrant ) or they are both negative ( in which case the 2 points are in the 4th quadrant )..

now the first statement says that xy>0.. so x and y have the same sign (they are either positve or negative ) .. that means (-x,y) is either in the 2nd or the 4th quadrant .. but since we dont know what is the positoin of (-a,b) and(-b,a) .. we dont have a defnite answer .. so not sufficient..

the second statement says that ax>0 .. again we have a,x and b (bcoz a and b have the same sign ) have the same sign ..but since we dont know the sign of y the statemant is insufficient..

now combine the 2 statements .. we have from the first statemnt x, y have the same sign ... from the 2nd statement we have a,x have the same sign .. so we get a,b,x,y have the same sign .. so now we can conclusively say that all the three points lie in the same quadrant ... if they are positive they will lie in the 3rd quadrant .. if they are negative the points will lie in the 4 th quadrant .. so the answer is C
Doesn't it matter that they already provide you with -ve signs for both a and b as x and y coordinates for the 2 points. If thats the case then we know for sure that the 2 point would be in the 2nd Quad...If there can be the possibility if being in 2 Quadrants why even give the 2 -ve signs, why didn't they just give (a,b) and (b,a)???
a,b,x,y are not specific numbers but r variables... hence can assume positive or negative values .....

gabriel Legendary Member
Joined
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Posted:
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Tue Apr 10, 2007 5:27 am
bicilotti wrote:
Two points (-a,b) (-b,a) are in the same quadrant of the xy plane. Is the point (-x,y) in the same plane?

(i) xy>0
(ii) ax>0

given that (-a ,b) and (-b,a) are in the same quadrant .. that means both a and b have tha same sign .. that is they are eoither both positive ( in which case the 2 points are both are in the second quadrant ) or they are both negative ( in which case the 2 points are in the 4th quadrant )..

now the first statement says that xy>0.. so x and y have the same sign (they are either positve or negative ) .. that means (-x,y) is either in the 2nd or the 4th quadrant .. but since we dont know what is the positoin of (-a,b) and(-b,a) .. we dont have a defnite answer .. so not sufficient..

the second statement says that ax>0 .. again we have a,x and b (bcoz a and b have the same sign ) have the same sign ..but since we dont know the sign of y the statemant is insufficient..

now combine the 2 statements .. we have from the first statemnt x, y have the same sign ... from the 2nd statement we have a,x have the same sign .. so we get a,b,x,y have the same sign .. so now we can conclusively say that all the three points lie in the same quadrant ... if they are positive they will lie in the 3rd quadrant .. if they are negative the points will lie in the 4 th quadrant .. so the answer is C

Thanked by: sachindia
guynoor Senior | Next Rank: 100 Posts
Joined
10 Feb 2007
Posted:
59 messages
1
Tue Apr 10, 2007 5:15 am
bicilotti wrote:
Quote:
I tought so, gmatprep says C...
Yeah its not A .... i guess i just hurried on the answer. Yes C is the right answer. Here the key is not to get confused by variables of the x and y co-ordinates. Try diagramming the figure and you can spot the answer easily. If you still have problems plug in some numbers for the variables which might make it easier to understand.

guynoor Senior | Next Rank: 100 Posts
Joined
10 Feb 2007
Posted:
59 messages
1
Tue Apr 10, 2007 5:11 am
guynoor wrote:
guynoor wrote:
bicilotti wrote:
Two points (-a,b) (-b,a) are in the same quadrant of the xy plane. Is the point (-x,y) in the same plane?

(i) xy>0
(ii) ax>0

Both (1) and (2) are alone sufficient...am i right?

guynoor Senior | Next Rank: 100 Posts
Joined
10 Feb 2007
Posted:
59 messages
1
Tue Apr 10, 2007 5:08 am
guynoor wrote:
bicilotti wrote:
Two points (-a,b) (-b,a) are in the same quadrant of the xy plane. Is the point (-x,y) in the same plane?

(i) xy>0
(ii) ax>0

Working on it...

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