Find all School-related info fast with the new School-Specific MBA Forum

It is currently 17 Sep 2014, 09:38

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Q. Is a^2*b > 0? 1) |a|=b 2) ab<0

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
SVP
SVP
User avatar
Joined: 30 Apr 2008
Posts: 1893
Location: Oklahoma City
Schools: Hard Knocks
Followers: 29

Kudos [?]: 433 [0], given: 32

GMAT Tests User
Q. Is a^2*b > 0? 1) |a|=b 2) ab<0 [#permalink] New post 07 Jul 2008, 11:48
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0
_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

Get the best GMAT Prep Resources with GMAT Club Premium Membership

1 KUDOS received
Intern
Intern
avatar
Joined: 29 May 2008
Posts: 24
Followers: 0

Kudos [?]: 4 [1] , given: 0

Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 11:59
1
This post received
KUDOS
According to me, the answer is C.

1) |a| = b, which means that b should be positive.
2) says that one of a or b should be negative.

From 1 we know that "b" is positive hence "a" should be negative and we know that a^2*b < 0.
1 KUDOS received
Manager
Manager
User avatar
Joined: 08 Jun 2008
Posts: 70
Followers: 1

Kudos [?]: 3 [1] , given: 0

Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 12:01
1
This post received
KUDOS
jallenmorris wrote:
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0


1. Insufficient: because a can be either 0 or any other number (+ve or -ve)
2. Insufficient: because ab < 0 gives us that one of them is -ve but we don't know which.

Combined: Sufficient: because from 1 & 2, b can't be -ve so a should be -ve and so a^2*b is > 0
It is C.
1 KUDOS received
Director
Director
avatar
Joined: 01 Jan 2008
Posts: 629
Followers: 3

Kudos [?]: 131 [1] , given: 1

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 12:04
1
This post received
KUDOS
jallenmorris wrote:
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0


1: insufficient a = b = 1 or a = b = 0 (b >=0)
2: insufficient a = 1, b = -1 or a = -1, b = 1 (a, b are not equal to 0)

1&2: since b >= 0 and b is not equal to zero -> b > 0, a is not equal to 0 -> a^2*b > 0 -> C
SVP
SVP
User avatar
Joined: 30 Apr 2008
Posts: 1893
Location: Oklahoma City
Schools: Hard Knocks
Followers: 29

Kudos [?]: 433 [0], given: 32

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 12:23
maratikus wrote:
jallenmorris wrote:
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0


1: insufficient a = b = 1 or a = b = 0 (b >=0)
2: insufficient a = 1, b = -1 or a = -1, b = 1 (a, b are not equal to 0)

1&2: since b >= 0 and b is not equal to zero -> b > 0, a is not equal to 0 -> a^2*b > 0 -> C


With respect to 1 & 2...You're saying neither A nor B can = 0 because anything * 0 = 0 and we're told in 2) that ab <0 (which is not zero). Then with 1, b = |a| and the absolute value of A cannot be nagative. So we know from the 2 statements that B is not 0, and it is not negative. That makes a be negative and not zero (not zero from #2).

Thanks. That helps me out a bunch. +1 for you.
_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

Get the best GMAT Prep Resources with GMAT Club Premium Membership

CEO
CEO
User avatar
Joined: 29 Mar 2007
Posts: 2593
Followers: 16

Kudos [?]: 189 [0], given: 0

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 13:30
jallenmorris wrote:
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0


1: a can be 0. Insuff.

2: b could be -. INsuff.

Together, suff b/c a is not 0.
Director
Director
avatar
Joined: 20 Sep 2006
Posts: 658
Followers: 2

Kudos [?]: 63 [0], given: 7

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 13:51
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0

From 1)

b must be possitive. a's value doesn't matter because a^2 is anyways going to be positive. So far 1) is suff but ... we dont know if a is a non zero or not. hence 1) is not suff.

From 2)

either a or b has to be negative. And neither a or b is zero.
if a is -ve and b is +ve then a^2*b > 0
if a is +ve and b is -ve then a^2*b < 0

therefore not sufficient

TOGETHER:

a and b not equal to zero.
b is +ve
a is -ve

Sufficient.

ANSWER: C
VP
VP
User avatar
Joined: 03 Apr 2007
Posts: 1377
Followers: 3

Kudos [?]: 178 [0], given: 10

GMAT Tests User Reviews Badge
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 17:00
jallenmorris wrote:
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0


Allen, please help me understand this :
a^2*b = (a^2)* b ?
or
a^2*b = a^(2* b) ?
Senior Manager
Senior Manager
avatar
Joined: 23 May 2006
Posts: 328
Followers: 2

Kudos [?]: 71 [0], given: 0

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 18:28
jallenmorris wrote:
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0


1. If a^(2b) then answer is C

2. If (a^2)b then answer is E

Please tell us which is the case - 1 or 2
SVP
SVP
User avatar
Joined: 30 Apr 2008
Posts: 1893
Location: Oklahoma City
Schools: Hard Knocks
Followers: 29

Kudos [?]: 433 [0], given: 32

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 19:12
I should not have copied and pasted, I should have used the math functionality provided by the forums.

goalsnr wrote:
jallenmorris wrote:
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0


Allen, please help me understand this :
a^2*b = (a^2)* b ?
or
a^2*b = a^(2* b) ?

_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Manager
Manager
avatar
Joined: 22 May 2007
Posts: 219
Followers: 2

Kudos [?]: 33 [0], given: 0

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 19:57
Well, C is the answer if a and b are integers.
Wouldn't the result be a complex number if a negative a were raised to a decimal power ? So E ????
Director
Director
avatar
Joined: 23 Sep 2007
Posts: 798
Followers: 5

Kudos [?]: 77 [0], given: 0

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 20:34
jallenmorris wrote:
Is a^2*b > 0?
1) |a|=b
2) ab<0


Is (a^2)*b > 0?


edit, C, forgot to consider that a can be 0
CEO
CEO
User avatar
Joined: 29 Aug 2007
Posts: 2501
Followers: 53

Kudos [?]: 506 [0], given: 19

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 07 Jul 2008, 22:28
jallenmorris wrote:
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0


good one. go for C as a in (1) could be 0.
_________________

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


GT

SVP
SVP
User avatar
Joined: 30 Apr 2008
Posts: 1893
Location: Oklahoma City
Schools: Hard Knocks
Followers: 29

Kudos [?]: 433 [0], given: 32

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 08 Jul 2008, 03:56
I've decided that when I get a DS like this, I'm going to consider a few numbers. I'm going to start with the following set:

{-2, -1, -0.5, 0, 0.5, 1, 2}

That should give an good indication as to how the inequality acts with both + and - numbers.
_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

Get the best GMAT Prep Resources with GMAT Club Premium Membership

VP
VP
User avatar
Joined: 03 Apr 2007
Posts: 1377
Followers: 3

Kudos [?]: 178 [0], given: 10

GMAT Tests User Reviews Badge
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 08 Jul 2008, 07:35
C

1. a>0,b>0 yes
a<0,b> 0 yes
a= b =0 no

insuff

2.a>0 b<0 no
a<0 b>0 yes

insuff

from 1 and 2
a< 0 b >0
Suff

C
Intern
Intern
avatar
Joined: 01 Jul 2008
Posts: 41
Followers: 1

Kudos [?]: 8 [0], given: 20

Re: Another DS question....probably not hard...I just don't know [#permalink] New post 10 Jul 2008, 02:36
x97agarwal wrote:
jallenmorris wrote:
Q. Is a^2*b > 0?
1) |a|=b
2) ab<0


1. If a^(2b) then answer is C

2. If (a^2)b then answer is E

Please tell us which is the case - 1 or 2


IMO for both cases viz. a^(2b) or (a^2)b the answer is C.

the solution:
a != 0 and b != 0 (a&b not equal to 0) from ab<0
& b>0 from |a|=b ---1
=> a<0
=> a^(2b)>0 ---2
& a^2>0 ---3

hence for the case
1. a^(2b) >0 from ---2
2. (a^2)b > 0 from ---1 & 3

Please correct me if i made a mistake.
Intern
Intern
avatar
Joined: 07 Jul 2008
Posts: 1
Followers: 0

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

Re: Another DS question....probably not hard...I just don't know [#permalink] New post 10 Jul 2008, 09:50
assuming we are working with a^(2b) > 0, and the following assumptions

B is not negative, B = |A|
A is negative since AB< 0

use -2, and -.5 for A. and 2,.5 for B respectively.

A = -2: (-2)^(2*2) = 16
A = -.5: (-.5)^(2*.5) = -.5

answers on both side of 0.....get E
Senior Manager
Senior Manager
avatar
Joined: 07 Jan 2008
Posts: 297
Followers: 1

Kudos [?]: 19 [0], given: 0

GMAT Tests User
Re: Another DS question....probably not hard...I just don't know [#permalink] New post 13 Jul 2008, 10:02
To prove, we need:
a) find out if a or b or both are zero?
b) Whether b is +ve or -ve.

1) b = |a| means b is non-negative i.e. either +ve or 0 - Insufficient.

2) ab<0 means a & b are not 0. but either a or b is -ve

Combining: we can say that b is +ve and a is -ve.
C.
Re: Another DS question....probably not hard...I just don't know   [#permalink] 13 Jul 2008, 10:02
    Similar topics Author Replies Last post
Similar
Topics:
(a^3)b+(a^2)(b^2)+a(b^3)>0? 1. ab>0 2. b<0 Creeper300 4 05 Nov 2010, 08:43
If b is positive, is ab positive? 1. a^2b>0 2. a^2+b=13 EnterMatrix 7 17 Jul 2010, 11:19
Is a^2*b > 0? 1) |a|=b 2) ab<0 iamba 5 17 Jun 2007, 20:58
If b is positive, is ab positive? 1)a^2b >0 2)a^2 + b=13 cucrose 2 27 Feb 2007, 16:37
If ab>0, does (a+2)(b+2) = 4? (1) ab = -2(a+b) (2) a=b coffeeloverfreak 7 10 Sep 2005, 14:06
Display posts from previous: Sort by

Q. Is a^2*b > 0? 1) |a|=b 2) ab<0

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.