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Are x and y both positive?

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Director
Joined: 07 Jun 2006
Posts: 513
Re: DS - x and y positive [#permalink]

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04 Jul 2006, 11:10
gidimba wrote:
Are x and y both positive?

1. 2x-2y=1
2. x/y >1

(1) x-y = 1/2, can't say if both are +ve (for e.g. 2,-1.5 or -1.5, -2) (INSUFF)
(2) x/y > 1 ; {-10, -5} or {10,5}. even combining both does not provide a definite answer.

(E)
Senior Manager
Joined: 11 May 2006
Posts: 258

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04 Jul 2006, 11:30
shahnandan wrote:
stmt 1,

x=o y= -1/2 NO
x=3 y=2 1/2 YES

insuff

stmt2

x>y both can be negative or positive -- insuff

together,

consider values for stmt1 as above--E.

x=0 and y = -1/2 do not satisfy x/y > 1
Senior Manager
Joined: 11 May 2006
Posts: 258
Re: DS - x and y positive [#permalink]

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04 Jul 2006, 11:33
necromonger wrote:
gidimba wrote:
Are x and y both positive?

1. 2x-2y=1
2. x/y >1

(1) x-y = 1/2, can't say if both are +ve (for e.g. 2,-1.5 or -1.5, -2) (INSUFF)
(2) x/y > 1 ; {-10, -5} or {10,5}. even combining both does not provide a definite answer.

(E)

(1) says x > y
(2) says x and y are either both +ve or both -ve.

considering both together,
if x > y, then both need to be +ve to satisfy x/y > 1
Senior Manager
Joined: 20 Feb 2006
Posts: 331

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04 Jul 2006, 14:16
haas_mba07 wrote:
gidimba,
Can we have the OA please?

1. x = y+1 , not suff
2. x/y>1 , not suff

using both.
(y+1)/y >1
1+(1/y) >1.

This means Y is +Ve. But X = y+1. so both x and y are +ve .. ==> C
Senior Manager
Joined: 20 Feb 2006
Posts: 331

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04 Jul 2006, 14:21
shahnandan wrote:
stmt 1,

x=o y= -1/2 NO
x=3 y=2 1/2 YES

insuff

stmt2

x>y both can be negative or positive -- insuff

together,

consider values for stmt1 as above--E.

x/y >1 doesn't mean X >Y.. For ex -5/-3 >1, but -5 isn't greater than -3.
CEO
Joined: 20 Nov 2005
Posts: 2894
Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008

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04 Jul 2006, 15:11
C

St1: This gives us x >y : INSUFF

St2: This gives us: Either both are +ve or both are -ve. If both +ve then x>y, but if both -ve then x < y. : INSUFF

Combined: Simply we get x > y and both are +ve : SUFF
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

Senior Manager
Joined: 08 Jun 2004
Posts: 495
Location: Europe

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05 Jul 2006, 01:03
Guys let me give you the OA.
OA is 'C'.
This is GMATPrep question.
Manager
Joined: 01 Jun 2006
Posts: 139

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05 Jul 2006, 01:33
(1) said that x>y
(2) said that x/y>1 so x,y must be both positive(x>y) or negative (x<y)
(1),(2) together we have x,y are both positive numbers.
Intern
Joined: 11 May 2004
Posts: 46
Location: USA

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05 Jul 2006, 13:49
THE OA is C i think i saw this in powerprep

All u do is

X=2 Y=1.5
or X=-1 Y= 1.5

B states X>Y, hence u can solve and only 1 solution X AND Y are POSTIIVE THUS C
GMAT Instructor
Joined: 04 Jul 2006
Posts: 1262

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07 Jul 2006, 04:17
Are x and y both positive?

1. 2x-2y=1
2. x/y >1

From (1) x-y=1/2>0 (not sufficient (x,y) could be (3/2,1) or (-2,-3/2) or (0,-1/2)... N. Suff

From (2), x and y are the same sign and x is further from 0 than is y.
(x,y) could be (3,1), (-3,-1)... N Suff

But together, x and y must be either both positive or both negative (from (2))

If x,y are both negative, x<y<0, so x-y<0, so 2(x-y) cannot be 1, which contradicts (1)

Therefore x any must both be positive Ans. C
Current Student
Joined: 28 Dec 2004
Posts: 3357
Location: New York City
Schools: Wharton'11 HBS'12

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07 Jul 2006, 12:58
OK lets see...

question stem is x AND y BOTH +

1) 2x-2y=1

2(x-y)=1; which can be written as x=1/2 + y

insuff... x can be -1 and y=-1.5 or x=1.5 and y=1

2) x/y > 1

well...DONT do anything like cross multiplication cause we dont know the signs of x or y. All we know is that X and Y have to have the same sign + or -ve. Insuff

lets take em together

sub vaule for x

1/2y + 1 > 1; well this can only be true if Y is +ve...if Y is +ve then X is +ve (given in statement 2)..

C it is....

Hope this helps..its a very simple way of lookin at this problem..and time efficient too, since i dont have to plug in numbers...
07 Jul 2006, 12:58

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