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

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

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New post 16 Oct 2008, 11:03
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If x and y are positive, is 3x>7y ?

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

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Re: DS- QUestion [#permalink]

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New post 16 Oct 2008, 12:06
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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Re: DS- QUestion [#permalink]

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New post 16 Oct 2008, 13:33
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

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Re: DS- QUestion [#permalink]

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New post 16 Oct 2008, 13:56
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.

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Re: DS- QUestion [#permalink]

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New post 16 Oct 2008, 14:18
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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Re: DS- QUestion [#permalink]

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New post 16 Oct 2008, 15:35
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.

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Re: DS- QUestion [#permalink]

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New post 16 Oct 2008, 16:04
[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

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Re: DS- QUestion [#permalink]

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New post 16 Oct 2008, 16:21
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.

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Re: DS- QUestion [#permalink]

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New post 17 Oct 2008, 01:19
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.

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Re: DS- QUestion [#permalink]

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New post 17 Oct 2008, 02:19
Unless the question has typo, the answer must be E.

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Re: DS- QUestion [#permalink]

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New post 17 Oct 2008, 10:33
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. :oops: :oops:
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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


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Re: DS- QUestion [#permalink]

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New post 19 Oct 2008, 04:51
rnemani wrote:
If x and y are positive, is 3x>7y ?

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


1) x>y+4 say 3x>4y+3y => x>y+4/3 y now if 4/3y<4 we are not sure whether 3x>7y holds good !!

INSUFFI

2)-5x<14y => 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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Re: DS- QUestion   [#permalink] 19 Oct 2008, 04:51
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If x and y are positive, is 3x>7y ? 1) x>y+4 2)

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