It is currently 23 Jun 2017, 09:11

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Is ab > 0?

Author Message
TAGS:

### Hide Tags

Manager
Joined: 10 Feb 2011
Posts: 113

### Show Tags

15 Feb 2011, 13:09
2
This post was
BOOKMARKED
00:00

Difficulty:

45% (medium)

Question Stats:

59% (02:07) correct 41% (00:40) wrong based on 64 sessions

### HideShow timer Statistics

Is ab > 0?

(1) a – b > 0
(2) a + b < 0
[Reveal] Spoiler: OA
Math Expert
Joined: 02 Sep 2009
Posts: 39607
Re: Is ab > 0? (1) a – b > 0. (2) a + b <0. [#permalink]

### Show Tags

15 Feb 2011, 13:39
2
KUDOS
Expert's post
1
This post was
BOOKMARKED
banksy wrote:
173. Is ab > 0?
(1) a – b > 0.
(2) a + b <0.

Note that:
You can only add inequalities when their signs are in the same direction:

If $$a>b$$ and $$c>d$$ (signs in same direction: $$>$$ and $$>$$) --> $$a+c>b+d$$.
Example: $$3<4$$ and $$2<5$$ --> $$3+2<4+5$$.

You can only apply subtraction when their signs are in the opposite directions:

If $$a>b$$ and $$c<d$$ (signs in opposite direction: $$>$$ and $$<$$) --> $$a-c>b-d$$ (take the sign of the inequality you subtract from).
Example: $$3<4$$ and $$5>1$$ --> $$3-5<4-1$$.

Back to the original question:

Is ab > 0?

Question basically asks whether $$a$$ and $$b$$ have the same sign.

(1) a – b > 0 --> $$a>b$$. Not sufficient to say whether $$a$$ and $$b$$ have the same sign.

(2) a + b <0 --> $$a<-b$$. Again not sufficient to say whether $$a$$ and $$b$$ have the same sign.

(1)+(2) subtract (2) from (1): $$(a-b)-(a+b)>0$$ --> $$b<0$$ --> but $$a$$ could still be positive or negative (or even zero), for example: $$a=-1$$ and $$b=-2$$ or $$a=1$$ and $$b=-2$$. Not sufficient.

Or: as from (1) $$b<a$$ and from (2) $$a<-b$$ then $$b<a<-b$$ --> $$a<|b|$$ --(b)-----0-----(-b)-- --> $$a$$ is somewhere between $$b$$ and $${-b}$$ so it can be positive, negative or zero). Not sufficient.

_________________
Senior Manager
Joined: 08 Nov 2010
Posts: 408
Re: Is ab > 0? (1) a – b > 0. (2) a + b <0. [#permalink]

### Show Tags

16 Feb 2011, 13:14
same trick as the other one you posted. good luck. thanks for posting.
_________________
Current Student
Status: Up again.
Joined: 31 Oct 2010
Posts: 533
Concentration: Strategy, Operations
GMAT 1: 710 Q48 V40
GMAT 2: 740 Q49 V42
Re: Is ab > 0? (1) a – b > 0. (2) a + b <0. [#permalink]

### Show Tags

17 Feb 2011, 23:52
banksy wrote:
173. Is ab > 0?
(1) a – b > 0.
(2) a + b <0.

Try picking numbers and applying them considering different possible scenarios.

(1) a-b > 0
Case 1. a= -2 b= -5
a-b=-2-(-5)= 3. Condition satified.
So is ab>0? Yes.

Case 2. A= 5, B=(-3)
a-b= 5-(-3)= 8. Condition satisfied.
So is ab>0? No.

2 different answers. Hence this statement is insufficient.

(2) a+b<0

Case 1. a=- -10 , b= -5.
a+b=(-10-5)=-15. Condition Satisfied.
So is ab>0? Yes.

Case 2. a= -10 , b= 5
a+b= (-10+5)=-5. Condition satisfied.
So is ab>0?. No.

Again, 2 different answers. Hence this statement is also not sufficient.

1&2 Combined: Not sufficient as we can pick any combination of positive/ negative numbers.

_________________

My GMAT debrief: http://gmatclub.com/forum/from-620-to-710-my-gmat-journey-114437.html

Math Expert
Joined: 02 Sep 2009
Posts: 39607
Re: Is ab > 0? [#permalink]

### Show Tags

23 Feb 2014, 05:11
Bumping for review and further discussion.
_________________
BSchool Forum Moderator
Joined: 12 Aug 2015
Posts: 2185
Re: Is ab > 0? [#permalink]

### Show Tags

13 Mar 2016, 07:44
The basic rule => If any linear algebraic equation contains one algebraic symbol => we can alter that
so there is no way we convert the + sign or the - sign to the * sign
hence E
Also B must be always negative (from combining the inequalities)
and A>0 or A<0 so AB>0 or AB<O
_________________

Give me a hell yeah ...!!!!!

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 15926
Re: Is ab > 0? [#permalink]

### Show Tags

22 Apr 2017, 09:28
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: Is ab > 0?   [#permalink] 22 Apr 2017, 09:28
Similar topics Replies Last post
Similar
Topics:
1 Is ab – c > 0? 2 21 Mar 2017, 08:25
2 Is ab+cd>0? 2 21 Nov 2016, 01:58
11 Is 0 > ab? 11 21 Aug 2016, 06:16
2 Is a/b > 0 ? 6 13 Mar 2016, 08:41
2 Is a/b > 0? 3 18 Jul 2016, 04:13
Display posts from previous: Sort by