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# If (a-b)/c<0, is a>b?

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Director
Joined: 03 Aug 2012
Posts: 899

Kudos [?]: 886 [0], given: 322

Concentration: General Management, General Management
GMAT 1: 630 Q47 V29
GMAT 2: 680 Q50 V32
GPA: 3.7
WE: Information Technology (Investment Banking)

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16 Mar 2013, 22:15
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Difficulty:

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Question Stats:

72% (00:59) correct 28% (01:28) wrong based on 64 sessions

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If (a-b)/c<0, is a>b?

(1) c < 0
(2) a + b < 0
[Reveal] Spoiler: OA

_________________

Rgds,
TGC!
_____________________________________________________________________
I Assisted You => KUDOS Please
_____________________________________________________________________________

Last edited by Bunuel on 17 Mar 2013, 01:37, edited 1 time in total.
Renamed the topic and edited the question.

Kudos [?]: 886 [0], given: 322

Director
Joined: 03 Aug 2012
Posts: 899

Kudos [?]: 886 [1], given: 322

Concentration: General Management, General Management
GMAT 1: 630 Q47 V29
GMAT 2: 680 Q50 V32
GPA: 3.7
WE: Information Technology (Investment Banking)

### Show Tags

16 Mar 2013, 22:20
1
KUDOS
(a-b)/c <0

=> c(a-b)/c^2 < 0
=> ac -bc <0
=> ac<bc

Statement (1) : Tells the sign of (C) means sufficient.

Statement (2) : a+b < 0

=> a < -b

a b a<-b Is a>b?
+ + Not Poss N/A
- - Yes No
- + Yes No
+ - Yes No

Why the answer is not (D).

Please tell what I am missing above

Rgds,
TGC
_________________

Rgds,
TGC!
_____________________________________________________________________
I Assisted You => KUDOS Please
_____________________________________________________________________________

Kudos [?]: 886 [1], given: 322

Math Expert
Joined: 02 Sep 2009
Posts: 41891

Kudos [?]: 128906 [1], given: 12183

Re: If (a-b)/c<0, is a>b? [#permalink]

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17 Mar 2013, 01:53
1
KUDOS
Expert's post
If (a-b)/c<0, is a>b?

(1) c < 0. Multiply (a-b)/c<0 by negative c and flip the sign a-b>0 --> a>b. Sufficient.

(2) a + b < 0. The sum of two numbers is less than zero. Can we tell which of them is greater? (Can we tell whether a>b or a<b?) No, consider a=1, b=-2 and c=-1 AND a=-2, b=1 and c=1. Not sufficient.

_________________

Kudos [?]: 128906 [1], given: 12183

VP
Status: Final Lap Up!!!
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Joined: 21 Sep 2012
Posts: 1077

Kudos [?]: 648 [1], given: 70

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WE: Engineering (Transportation)

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17 Mar 2013, 09:38
1
KUDOS
targetgmatchotu wrote:
Bunuel wrote:
targetgmatchotu wrote:
(a-b)/c <0

=> c(a-b)/c^2 < 0
=> ac -bc <0
=> ac<bc

Statement (1) : Tells the sign of (C) means sufficient.

Statement (2) : a+b < 0

=> a < -b

a b a<-b Is a>b?
+ + Not Poss N/A
- - Yes No
- + Yes No
+ - Yes No

Why the answer is not (D).

Please tell what I am missing above

Rgds,
TGC

Consider one of the cases in your approach above: if both a and b are negative, it's possible that a>b as well as a<b. For example, a=-1, b=-2, and c=-1 AND a=-2, b=-1, and c=1.

Hope it helps.

Why to take c variable in picture .

Given that a<-b
I think appropriate would be
a = -1
b = -2 (here a>b still holding a<-b)

a = -2
b = -1 (here a <b still holding a<-b)

Hence,wrong

Hi TGC
good to see you back on the forums..........people gather courage from life's storms.

I think the process you suggested is correct and has got no flaws in it....its concise...i do not find any use of third variable here.

Archit

Kudos [?]: 648 [1], given: 70

Intern
Joined: 05 Mar 2013
Posts: 1

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

Re: If (a-b)/c<0, is a>b? [#permalink]

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17 Mar 2013, 01:46
Before cross multiplying or multiplying numerator and denominator by c you should keep in mind that c should not be equal to 0
So which statement proves c won't be 0
(1) c < 0
This statement implies that c is not equal to 0
(2) a + b < 0
You aren't sure whether c would be 0 or not.
Hence, the answer should be A

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

Director
Joined: 03 Aug 2012
Posts: 899

Kudos [?]: 886 [0], given: 322

Concentration: General Management, General Management
GMAT 1: 630 Q47 V29
GMAT 2: 680 Q50 V32
GPA: 3.7
WE: Information Technology (Investment Banking)
Re: If (a-b)/c<0, is a>b? [#permalink]

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17 Mar 2013, 07:14
Bunuel wrote:
If (a-b)/c<0, is a>b?

(1) c < 0. Multiply (a-b)/c<0 by negative c and flip the sign a-b>0 --> a>b. Sufficient.

(2) a + b < 0. The sum of two numbers is less than zero. Can we tell which of them is greater? (Can we tell whether a>b or a<b?) No, consider a=1, b=-2 and c=-1 AND a=-2, b=1 and c=1. Not sufficient.

What is wrong in the solution that I gave?

Rgds,
TGC
_________________

Rgds,
TGC!
_____________________________________________________________________
I Assisted You => KUDOS Please
_____________________________________________________________________________

Kudos [?]: 886 [0], given: 322

Math Expert
Joined: 02 Sep 2009
Posts: 41891

Kudos [?]: 128906 [0], given: 12183

### Show Tags

17 Mar 2013, 07:54
targetgmatchotu wrote:
(a-b)/c <0

=> c(a-b)/c^2 < 0
=> ac -bc <0
=> ac<bc

Statement (1) : Tells the sign of (C) means sufficient.

Statement (2) : a+b < 0

=> a < -b

a b a<-b Is a>b?
+ + Not Poss N/A
- - Yes No
- + Yes No
+ - Yes No

Why the answer is not (D).

Please tell what I am missing above

Rgds,
TGC

Consider one of the cases in your approach above: if both a and b are negative, it's possible that a>b as well as a<b. For example, a=-1, b=-2, and c=-1 AND a=-2, b=-1, and c=1.

Hope it helps.
_________________

Kudos [?]: 128906 [0], given: 12183

Director
Joined: 03 Aug 2012
Posts: 899

Kudos [?]: 886 [0], given: 322

Concentration: General Management, General Management
GMAT 1: 630 Q47 V29
GMAT 2: 680 Q50 V32
GPA: 3.7
WE: Information Technology (Investment Banking)

### Show Tags

17 Mar 2013, 09:10
Bunuel wrote:
targetgmatchotu wrote:
(a-b)/c <0

=> c(a-b)/c^2 < 0
=> ac -bc <0
=> ac<bc

Statement (1) : Tells the sign of (C) means sufficient.

Statement (2) : a+b < 0

=> a < -b

a b a<-b Is a>b?
+ + Not Poss N/A
- - Yes No
- + Yes No
+ - Yes No

Why the answer is not (D).

Please tell what I am missing above

Rgds,
TGC

Consider one of the cases in your approach above: if both a and b are negative, it's possible that a>b as well as a<b. For example, a=-1, b=-2, and c=-1 AND a=-2, b=-1, and c=1.

Hope it helps.

Why to take c variable in picture .

Given that a<-b
I think appropriate would be
a = -1
b = -2 (here a>b still holding a<-b)

a = -2
b = -1 (here a <b still holding a<-b)

Hence,wrong
_________________

Rgds,
TGC!
_____________________________________________________________________
I Assisted You => KUDOS Please
_____________________________________________________________________________

Kudos [?]: 886 [0], given: 322

Re: Inequalities   [#permalink] 17 Mar 2013, 09:10
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