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If x and y are positive, is 3x>7y ? 1) x>y+4 2)

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Intern
Joined: 22 Jul 2008
Posts: 42
If x and y are positive, is 3x>7y ? 1) x>y+4 2) [#permalink]

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16 Oct 2008, 12:03
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If x and y are positive, is 3x>7y ?

1) x>y+4
2) -5x<14y

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
SVP
Joined: 29 Aug 2007
Posts: 2426
Re: DS- QUestion [#permalink]

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16 Oct 2008, 13:06
spiridon wrote:
E
why?
rnemani wrote:
If x and y are positive, is 3x>7y ?

1) x>y+4
2) -5x<14y

from 2:

5x > 14y
2.5x > 7y

is not that suff?
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Intern
Joined: 22 Jul 2008
Posts: 42
Re: DS- QUestion [#permalink]

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16 Oct 2008, 14:33
I got B as -5x < -14y can be solved to x >14/5 y which show that x> 7/3y.

But the OA is D.
I am not sure how
Manager
Joined: 14 Oct 2008
Posts: 158
Re: DS- QUestion [#permalink]

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16 Oct 2008, 14:56
D is correct.

we have to prove x > 7/3 y
Case 1: x> y+4
y = 0 x > 4 means x > (7/3)* 0 , y=1, x> 5 means x >(7/3 ) * 1 etc... its sufficient.
Case 2: x > -14/5 y
it can be similarly proven using values .... that its sufficient.
hence D.
SVP
Joined: 29 Aug 2007
Posts: 2426
Re: DS- QUestion [#permalink]

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16 Oct 2008, 15:18
gameCode wrote:
D is correct.

we have to prove x > 7/3 y
Case 1: x> y+4
y = 0 x > 4 means x > (7/3)* 0 , y=1, x> 5 means x >(7/3 ) * 1 etc... its sufficient.
Case 2: x > -14/5 y
it can be similarly proven using values .... that its sufficient.
hence D.

how is st. 1 true?

if y = 1, x > 5, then 3x is 15 and 7y is 7. so 3x>7y is true.
but if y = 10, x > 14. lets say x = 15
3x is 45, where as 7y is 70.
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Senior Manager
Joined: 21 Apr 2008
Posts: 265
Location: Motortown
Re: DS- QUestion [#permalink]

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16 Oct 2008, 16:35
GMAT TIGER wrote:
spiridon wrote:
E
why?
rnemani wrote:
If x and y are positive, is 3x>7y ?

1) x>y+4
2) -5x<14y

from 2:

5x > 14y
2.5x > 7y

is not that suff?

how did you get 5x >14y from -5x<14y
even if you multiply with -1, you will get 5x >-14y

eg: x = 2, y=1
-10<14 - TRUE
10>-14 - TRUE

I get E for this question. I am suprised that the OA is D.
Retired Moderator
Joined: 05 Jul 2006
Posts: 1734
Re: DS- QUestion [#permalink]

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16 Oct 2008, 17:04
[quote="rnemani"]If x and y are positive, is 3x>7y ?

1) x>y+4
2) -5x<14y

from 1

( as an extreme measure , though it is mentioned that x,y are+ve i will use y = 0)

from 1

x> 4, say = 5 thus sure 3x>7y...........suff

from 2

5x> 14y ( i will approx devide by 5)

x> 3y ie: 3x>9y thus sure 3x> 7y..........suff

D
Senior Manager
Joined: 21 Apr 2008
Posts: 265
Location: Motortown
Re: DS- QUestion [#permalink]

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16 Oct 2008, 17:21
yezz wrote:
rnemani wrote:
If x and y are positive, is 3x>7y ?

1) x>y+4
2) -5x<14y

from 1

( as an extreme measure , though it is mentioned that x,y are+ve i will use y = 0)

from 1

x> 4, say = 5 thus sure 3x>7y...........suff

from 2

5x> 14y ( i will approx devide by 5)

x> 3y ie: 3x>9y thus sure 3x> 7y..........suff

D

how about when x = 10, y = 5
30 < 35 - Not sufficient.
Manager
Joined: 14 Oct 2008
Posts: 158
Re: DS- QUestion [#permalink]

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17 Oct 2008, 02:19
yup i agree. Statement 1 is true only for y = 1, 2, 3. From 4 onwards its false. Hence its not sufficient.
Sorry for the earlier post.
VP
Joined: 17 Jun 2008
Posts: 1477
Re: DS- QUestion [#permalink]

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17 Oct 2008, 03:19
Unless the question has typo, the answer must be E.
SVP
Joined: 29 Aug 2007
Posts: 2426
Re: DS- QUestion [#permalink]

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17 Oct 2008, 11:33
LiveStronger wrote:
GMAT TIGER wrote:
spiridon wrote:
E
why?
rnemani wrote:
If x and y are positive, is 3x>7y ?

1) x>y+4
2) -5x<14y

from 2:

5x > 14y
2.5x > 7y

is not that suff?

how did you get 5x >14y from -5x<14y
even if you multiply with -1, you will get 5x >-14y

eg: x = 2, y=1
-10<14 - TRUE
10>-14 - TRUE

I get E for this question. I am suprised that the OA is D.

That I sometime do overlooking.
_________________

Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html
Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html
Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

VP
Joined: 17 Jun 2008
Posts: 1285
Re: DS- QUestion [#permalink]

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19 Oct 2008, 05:51
[quote="rnemani"]If x and y are positive, is 3x>7y ?

1) x>y+4
2) -5xy+4 say 3x>4y+3y => x>y+4/3 y now if 4/3y7y holds good !!

INSUFFI

2)-5x x> -14/5y

now if this is true and y>0 => x>7/3y may o may not be true !!
INSUFFI

Consider both :
1) and 2) say x>y+4 since this the positive among the two ,represents overlaping values hence INSUFI to validate the questioin
IMO E

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If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

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Re: DS- QUestion   [#permalink] 19 Oct 2008, 05:51
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