Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack
GMAT Club

 It is currently 30 Mar 2017, 09:56

Happening Now:

R2 Admission Decisions from Wharton: Join Chat Room 3

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

M11 #26

Author Message
Manager
Joined: 07 Jan 2008
Posts: 86
Followers: 2

Kudos [?]: 179 [1] , given: 1

Show Tags

24 Jan 2009, 14:18
1
KUDOS
3
This post was
BOOKMARKED
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Is $$A^7 B^2 C^3 > 0$$ ?

1. $$BC < 0$$
2. $$AC > 0$$

Source: GMAT Club Tests - hardest GMAT questions
Current Student
Joined: 28 Dec 2004
Posts: 3382
Location: New York City
Schools: Wharton'11 HBS'12
Followers: 15

Kudos [?]: 289 [5] , given: 2

Show Tags

24 Jan 2009, 14:38
5
KUDOS
i will go with C

1) tells us that either C or B is <0

insuff we dont know about A..

2) AC>0 good...we dont know if B=0

together sufficient..we know B is not 0 and AC>0
Math Expert
Joined: 02 Sep 2009
Posts: 37701
Followers: 7418

Kudos [?]: 100034 [4] , given: 11136

Show Tags

25 Apr 2012, 21:53
4
KUDOS
Expert's post
charlemagne wrote:
ilhom1986 wrote:
From the given question I found that
IF A>0 than C>0
IF A<0 than C<0

(I answered this question in less than a minute and choose B, because I
didn't consider B to be equal to zero)

Good question for GMAT starter, easy to get into trap...

I did this sometime back...bt I dont seem to have considered that B may be equal to 0, and still chose C.

CAn anyone show how B=0 case make a difference?

Sure. For example if we put $$b\neq{0}$$ in the stem then the answer would become B, instead of C.

IF THE QUESTION WERE:

If $$b\neq{0}$$ is $$a^7*b^2*c^3>0$$ ?

Since $$b\neq{0}$$ then $$b^2>0$$, so we can reduce by it (b^2 does not affect given inequality at all) and the question becomes: is $$a^7*c^3>0$$? So, the question basically asks whether $$a$$ and $$c$$ have the same sign. (Notice that if $$b\neq{0}$$ were not given then $$b^2\geq{0}$$, and we could not reduce by it)

(1) $$bc<0$$. Not sufficient.

(2) $$ac>0$$ --> $$a$$ and $$c$$ have the same sign. Sufficient.

Hope it's clear.

P.S. Solution to he original question is given here: m11-75085.html#p1073868
_________________
Manager
Joined: 15 Sep 2009
Posts: 137
Followers: 1

Kudos [?]: 23 [1] , given: 2

Show Tags

14 Apr 2010, 23:39
1
KUDOS
statement 1 :
==========
We can get combinations of B & C bt no clue abt A.So insuff

Statement 2:
==========
We can get combinations about A & C bt no clue abt B.So insuff

Combining both we get
Case 1:
======
A -ve
C -ve
B +ve

For the above combination,we get the answer as YES

Case 2:
======
A +ve
C +ve
B -ve

For case 2 combination also we get the answer as YES.

So I will go with option C

-Deepak.
Math Expert
Joined: 02 Sep 2009
Posts: 37701
Followers: 7418

Kudos [?]: 100034 [1] , given: 11136

Show Tags

15 Apr 2012, 00:51
1
KUDOS
Expert's post
topmbaseeker wrote:
Is $$A^7 B^2 C^3 > 0$$ ?

1. $$BC < 0$$
2. $$AC > 0$$

[Reveal] Spoiler: OA
C

Source: GMAT Club Tests - hardest GMAT questions

Inequality $$a^7*b^2*c^3>0$$ to be true $$a$$ and $$c$$ must be either both positive or both negative AND $$b$$ must not be zero (in order $$a^7*b^2*c^3$$ not to equal to zero).

(1) $$bc<0$$ --> $$b\neq{0}$$. Don't know about $$a$$ and $$c$$. Not sufficient.

(2) $$ac>0$$ --> $$a$$ and $$c$$ are either both positive or both negative. Don't know about $$b$$. Not sufficient.

(1)+(2) Sufficient.

Hope it helps.
_________________
Math Expert
Joined: 02 Sep 2009
Posts: 37701
Followers: 7418

Kudos [?]: 100034 [1] , given: 11136

Show Tags

21 Apr 2012, 10:41
1
KUDOS
Expert's post
harshavmrg wrote:
topmbaseeker wrote:
Is $$A^7 B^2 C^3 > 0$$ ?

1. $$BC < 0$$
2. $$AC > 0$$

[Reveal] Spoiler: OA
C

Source: GMAT Club Tests - hardest GMAT questions

i followed graph method( it takes time, i dont know any easier method to do this), i got the answer C

Easier method is given here: m11-75085.html#p1073868

Similar questions to practice:
is-x-2-y-5-z-0-1-xz-y-0-2-y-z-98341.html
is-x-7-y-2-z-3-0-1-yz-0-2-xz-127692.html
m21-q30-96613.html

Hope it helps.
_________________
Manager
Status: Married
Joined: 30 Oct 2010
Posts: 65
Location: India
Concentration: Marketing, Finance
GMAT 1: 710 Q49 V38
GPA: 2.9
WE: Information Technology (Computer Software)
Followers: 2

Kudos [?]: 15 [1] , given: 40

Show Tags

22 Apr 2012, 20:15
1
KUDOS
topmbaseeker wrote:
Is $$A^7 B^2 C^3 > 0$$ ?

1. $$BC < 0$$
2. $$AC > 0$$

[Reveal] Spoiler: OA
C

Source: GMAT Club Tests - hardest GMAT questions

1. BC < 0 implies either B or C is negative, but not both
2. AC > 0 implies neither A nor C are negative, but both A and C may be negative

Using both 1 and 2, we have two options:

I - A is negative; B is positive; C is negative => $$A^7 B^2 C^3 > 0$$ is positive
II - A is positive; B is negative; C is positive => $$A^7 B^2 C^3 > 0$$ is positive

Hence Option C.! :D
_________________

KUDOS-ing does'nt cost you anything, but might just make someone's day!!!

"Musings of a Muddled Muggle Mind"
http://felinesmile.blogspot.in/

Math Expert
Joined: 02 Sep 2009
Posts: 37701
Followers: 7418

Kudos [?]: 100034 [1] , given: 11136

Show Tags

26 Apr 2012, 22:58
1
KUDOS
Expert's post
charlemagne wrote:

Yes....much clearer....Thank you!!!

Another kudos to you....
BTW, with so many of these already on your name, you must be going crazy with the amount of auto-notification emails coming your way??

That's not a problem.

Also one should consider kudos not only as a "thank you" to user whose post was helpful, but also as a tool to distinguish a valuable post. Notice that posts with more than 1 kudos have different color, also notice that total # of kudos is shown just beside the topic name, so by giving a kudos to a post you are drawing an attention of other users to the helpful material and thus are contributing to the community.
_________________
Math Expert
Joined: 02 Sep 2009
Posts: 37701
Followers: 7418

Kudos [?]: 100034 [1] , given: 11136

Show Tags

23 Apr 2013, 06:59
1
KUDOS
Expert's post
vshrivastava wrote:
I'm sorry if I'm missing something, but I think the right answer is B.

Here is how: Question: Is (A^7) * (B^2) * (C^3) > 0?

Statement 1: BC < 0
Evaluate the Y/N question:
Is (A^7) * (B*C)^2 * (C) > 0?
(B*C)^2 > 0
But, if A > 0 and C > 0 then expression > 0 => Yes
However, if A > 0 and C < 0 then expression < 0 => No
So, S1 is not sufficient. Eliminate A and D.

Statement 2: AC > 0
Evaluate the Y/N question:
Is (A^7) * (B^2) * (C^3) > 0?

Combine A and C.

Is (A*C)^3 * A^4 * B^2 > 0

S2 says A*C > 0 ; so (A*C)^3 > 0
A^4 is always positive even if A were negative; so A^4 > 0
B^2 is always positive even if B were negative; so B^2 > 0

So, the expression is always positive even if A and/or B were negative.
S2 is sufficient.

B is correct.

What do you guys think?

Notice that when we consider the second statement we know nothing about the value of b, so if b=0, then $$a^7*b^2*c^3=0$$ ($$a^7*b^2*c^3$$ is NOT greater than 0). That's why (2) is not sufficient.

Similar questions to practice:
is-x-2-y-5-z-0-1-xz-y-0-2-y-z-98341.html
is-x-7-y-2-z-3-0-1-yz-0-2-xz-127692.html
m21-q30-96613.html

Hope it helps.
_________________
Manager
Joined: 04 Jan 2009
Posts: 241
Followers: 1

Kudos [?]: 12 [0], given: 0

Show Tags

24 Jan 2009, 17:16
topmbaseeker wrote:
Is $$A^7 B^2 C^3 \gt 0$$ ?

1. $$BC \lt 0$$
2. $$AC \gt 0$$

(C) 2008 GMAT Club - m11#26

* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient

both will be reqd. just need to determine if both are adequate.
B^2*C^2>0
AC>0
So AB^2C^3>0
Now, A is also nonzero from 2.
So, A^6>0
Thus,
A^6*A*B^2*C^3>0
Hence, sufficient. C.
_________________

-----------------------
tusharvk

Intern
Joined: 18 Dec 2009
Posts: 3
Followers: 0

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

Show Tags

14 Apr 2010, 07:57
A^7B^2C^3 >0

1.BC<0
2.AC>0

sol 1
assume B>0 C<0 then BC<0

if C<0, A also <0 bcs AC>0 from 1&2 A^7B^2C^3 >0

Assume B<0 C>0 then BC<0

if C>0, A also >0 bcs AC>0 from 1&2 A^7B^2C^3 >0
Intern
Joined: 05 Jan 2010
Posts: 21
Followers: 0

Kudos [?]: 14 [0], given: 4

Show Tags

14 Apr 2010, 09:59
My pick is C

Must have both statements to ensure that (1.) at least 1 variable is > 0 (2.) none of the other variables = 0
Director
Joined: 25 Aug 2007
Posts: 950
WE 1: 3.5 yrs IT
WE 2: 2.5 yrs Retail chain
Followers: 77

Kudos [?]: 1293 [0], given: 40

Show Tags

15 Apr 2010, 02:02
IMO C.

A^7B^2C^3 can be reduced to AC as whatever be the value of B, B^2 will always be >0 while A and C have odd powers.

1) BC<0 (Insufficient) as we dont know the value of A.
2) AC>0 (InSufficient) as discussed above.

AC can be >0 only if both A and C are +ve or are -ve, but wait what if B=0.

I hope this helps.
_________________

Tricky Quant problems: http://gmatclub.com/forum/50-tricky-questions-92834.html
Important Grammer Fundamentals: http://gmatclub.com/forum/key-fundamentals-of-grammer-our-crucial-learnings-on-sc-93659.html

Manager
Status: On my way !!!
Joined: 11 Apr 2011
Posts: 115
Location: France
Concentration: Operations, Strategy
GMAT 1: 760 Q50 V44
GPA: 3.1
WE: Manufacturing and Production (Energy and Utilities)
Followers: 2

Kudos [?]: 14 [0], given: 4

Show Tags

18 Apr 2011, 05:32
Considering only 1. since BC < 0 we dont know about A
for 2. AC>0 (both negative or both positive) but B could be zero.

If we take both 1. and 2. -
if C < 0, B > 0 and A < 0 therefore $$A^7B^2C^3 > 0$$
if C > 0, B < 0 and A > 0 and still $$A^7B^2C^3 > 0$$

_________________

http://pyarapopat.wordpress.com

Intern
Joined: 14 Apr 2011
Posts: 22
GMAT 1: 750 Q49 V44
GPA: 3.7
Followers: 0

Kudos [?]: 10 [0], given: 23

Show Tags

18 Apr 2011, 18:36
I simplified this equation to A*B^2*C > 0 to make it slightly less daunting. B will always be positive unless it is zero.

1) BC < 0 means either B or C is Negative, but they can't both be negative. Also, neither can be zero. No other clues are given about A. Insufficient.
2) AC > 0 means A and C are either both negative or both positive. Can't be zero. Insufficient.

(2) states that the product of AC is always positive, since B^2 is also always positive and B isn't zero, then the equation must be positive. (C) is the answer.
_________________

"What we obtain too cheap, we esteem too lightly."
-Thomas Paine

SVP
Joined: 16 Nov 2010
Posts: 1671
Location: United States (IN)
Concentration: Strategy, Technology
Followers: 33

Kudos [?]: 528 [0], given: 36

Show Tags

18 Apr 2011, 19:24
I too had missed that B could be equal to 0 in (2).
(1) says :

BC < 0, So B is +ve and C is -ve, or B is -ve and C is +ve, we don't know about A, so not sufficient

(2)

AC > 0, so odd powers of A * odd powers of C are > 0

Because A^7 * C^3 = (AC)^3 * A^4 (AC is +ve and A^4 is always +ve)

B^2 is always non-negative, but B can be equal to 0, so not sufficient.

(1) and (2)

(1) indicates B is non-zero

So A^7 * B^2 * C^3 > 0

_________________

Formula of Life -> Achievement/Potential = k * Happiness (where k is a constant)

GMAT Club Premium Membership - big benefits and savings

Director
Joined: 01 Feb 2011
Posts: 755
Followers: 14

Kudos [?]: 120 [0], given: 42

Show Tags

20 Apr 2011, 18:06
(A^7 B^2 C^3)>0?

1. Not sufficient as we dont know anything about A. (B<0,C>0 or B>0 , C<0)

2. Not sufficient as we dont know anything about B. ( A>0,C>0 or A<0, C<0)

Together we have B<0 , C>0 , A>0 (case 1) or B> 0 , C<0, A<0(Case 2)

In both the cases we have (A^7 B^2 C^3)>0. So thats sufficient.

Intern
Joined: 01 Apr 2012
Posts: 20
Followers: 1

Kudos [?]: 6 [0], given: 10

Show Tags

15 Apr 2012, 00:39
Here 3 unknown in equations i.e. A, B and C.
so to solve this equations require details of all three.
(1) statement 1 provides information about B and C
(2) Statement 2 provides information about A and C

Over all by multiplication using statement 1 and 2 we can get the answers.

Manager
Status: I will not stop until i realise my goal which is my dream too
Joined: 25 Feb 2010
Posts: 234
Schools: Johnson '15
Followers: 2

Kudos [?]: 51 [0], given: 16

Show Tags

21 Apr 2012, 06:42
topmbaseeker wrote:
Is $$A^7 B^2 C^3 > 0$$ ?

1. $$BC < 0$$
2. $$AC > 0$$

[Reveal] Spoiler: OA
C

Source: GMAT Club Tests - hardest GMAT questions

i followed graph method( it takes time, i dont know any easier method to do this), i got the answer C
_________________

Regards,
Harsha

Note: Give me kudos if my approach is right , else help me understand where i am missing.. I want to bell the GMAT Cat

Satyameva Jayate - Truth alone triumphs

Manager
Joined: 23 Aug 2011
Posts: 83
Followers: 3

Kudos [?]: 210 [0], given: 13

Show Tags

23 Apr 2012, 07:48
I will split the question as
[(A)^6]*[(BC)^2]*(AC)

So (BC)^2>0 or =0
A^6>0 or =0
AC can be either >0 <0 or 0

so {[(A)^6]*[(BC)^2]*(AC)} will look like {(+/0) * (+/0) *(+/-/0)}

1:)BC<0 =>[(BC)^2]>0 but we are unsure about AC wheter its >0 or <0 so reject

strike off options A,D

Remaining options B,C,E

2.)AC>0 now this implies
[(A)^6]>0 (as A,C!=0)
[(BC)^2]>=0(we are unsure of B, whether its 0 or not)
(AC)>0
so result will be >=0, but its insufficient, as its not >0 but we have dual case of >=0

Strike off option B

options E,C are left, lets go for C ,combining
BC<0 and AC>0
implies that
[(BC)^2]>0
[(A)^6]>0
[AC]>0 so end result will be >0

So C is the ANS...
_________________

Whatever one does in life is a repetition of what one has done several times in one's life!
If my post was worth it, then i deserve kudos

Re: M11 #26   [#permalink] 23 Apr 2012, 07:48

Go to page    1   2    Next  [ 33 posts ]

Similar topics Replies Last post
Similar
Topics:
18 m11 06 19 08 Feb 2009, 17:30
13 m11#30 20 31 Dec 2008, 22:20
m11,#8 13 11 Nov 2008, 23:35
24 m11#9 9 01 Nov 2008, 08:23
2 M11 #03 2 01 Oct 2008, 15:20
Display posts from previous: Sort by

M11 #26

Moderator: Bunuel

 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®.