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

 It is currently 25 Sep 2016, 00:30

### 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 (x^7)(y^2)(z^3)>0?

Author Message
TAGS:

### Hide Tags

Intern
Joined: 19 Sep 2010
Posts: 26
Followers: 0

Kudos [?]: 78 [0], given: 0

### Show Tags

30 Sep 2010, 06:09
00:00

Difficulty:

65% (hard)

Question Stats:

35% (01:31) correct 65% (00:37) wrong based on 79 sessions

### HideShow timer Statistics

Is (x^7)(y^2)(z^3)>0?

(1) yz<0
(2) xz>0

[Reveal] Spoiler:
From GMAT Club Test - m25 - Q34

The OA is C but I think it's E
Statement (1) : clearly insufficient since we don't have the sign of Z (since it has an odd exponent)
Statement (2) : clearly insufficient since Y can be 0
Both (1) and (2) : well yes Y can't be 0 but we still can't tell the sign of Z ! Consider this example : X=4 , Y= -1, Z= -1 ; we will have both statements right but the original expression will be negative

Am I wrong ?
[Reveal] Spoiler: OA
Math Expert
Joined: 02 Sep 2009
Posts: 34817
Followers: 6476

Kudos [?]: 82544 [2] , given: 10107

### Show Tags

30 Sep 2010, 06:23
2
KUDOS
Expert's post
1
This post was
BOOKMARKED
Barkatis wrote:
From GMAT Club Test - m25 - Q34

Is $$(x^7)(y^2)(z^3) \gt 0$$ ?

1. $$yz \lt 0$$
2. $$xz \gt 0$$

The OA is C but I think it's E
Statement (1) : clearly insufficient since we don't have the sign of Z (since it has an odd exponent)
Statement (2) : clearly insufficient since Y can be 0
Both (1) and (2) : well yes Y can't be 0 but we still can't tell the sign of Z ! Consider this example : X=4 , Y= -1, Z= -1 ; we will have both statements right but the original expression will be negative

Am I wrong ?

Inequality $$x^7*y^2*z^3>0$$ to be true:
I. $$x$$ and $$z$$ must be either both positive or both negative, AND II. $$y$$ must not be zero.

(1) $$yz<0$$ --> $$y\neq{0}$$ (II is satisfied). Don't know about $$x$$ and $$z$$. Not sufficient.

(2) $$xz>0$$ --> $$x$$ and $$z$$ are either both positive or both negative (I is satisfied). Don't know about $$y$$. Not sufficient.

(1)+(2) Both conditions are satisfied. Sufficient.

As for your doubt: we are not interested in the sign of $$z$$, we need $$x$$ and $$z$$ to be be either both positive or both negative. Next, your example is not valid: x=4, y=-1, z=-1 --> yz=4>0 and xz=-4<0 and we are given that $$yz<0$$ and $$xz>0$$.

Hope it helps.
_________________
Intern
Joined: 19 Sep 2010
Posts: 26
Followers: 0

Kudos [?]: 78 [0], given: 0

### Show Tags

30 Sep 2010, 06:28
Am sorry, in the question is it x exponent z or the product between x and z ??
Math Expert
Joined: 02 Sep 2009
Posts: 34817
Followers: 6476

Kudos [?]: 82544 [0], given: 10107

### Show Tags

30 Sep 2010, 06:33
Barkatis wrote:
Am sorry, in the question is it x exponent z or the product between x and z ??

It's product: $$y*z<0$$ and $$x*z>0$$.
_________________
CEO
Status: Nothing comes easy: neither do I want.
Joined: 12 Oct 2009
Posts: 2795
Location: Malaysia
Concentration: Technology, Entrepreneurship
Schools: ISB '15 (M)
GMAT 1: 670 Q49 V31
GMAT 2: 710 Q50 V35
Followers: 222

Kudos [?]: 1531 [1] , given: 235

### Show Tags

30 Sep 2010, 06:34
1
KUDOS
Barkatis wrote:
Am sorry, in the question is it x exponent z or the product between x and z ??

It is the product.

Is $$(x^7)(y^2)(z^3) \gt 0$$ ? reduced to is Is $$(x)(y^2)(z) \gt 0$$ ? -> I have removed the squared values as they do not play any role in changing the sign, but I kept $$y^2$$ to consider the y=0 condition.
_________________

Fight for your dreams :For all those who fear from Verbal- lets give it a fight

Money Saved is the Money Earned

Jo Bole So Nihaal , Sat Shri Akaal

GMAT Club Premium Membership - big benefits and savings

Gmat test review :
http://gmatclub.com/forum/670-to-710-a-long-journey-without-destination-still-happy-141642.html

Intern
Joined: 19 Sep 2010
Posts: 26
Followers: 0

Kudos [?]: 78 [0], given: 0

### Show Tags

30 Sep 2010, 06:53
Bunuel wrote:
Barkatis wrote:
Am sorry, in the question is it x exponent z or the product between x and z ??

It's product: $$y*z<0$$ and $$x*z>0$$.

Ah oki ! Thanks I didn't pay attention to that
Senior Manager
Joined: 25 Feb 2010
Posts: 481
Followers: 4

Kudos [?]: 79 [0], given: 10

### Show Tags

30 Sep 2010, 15:30
Bunuel wrote:
From GMAT Club Test - m25 - Q34

Inequality $$x^7*y^2*z^3>0$$ to be true:
I. $$x$$ and $$z$$ must be either both positive or both negative, AND II. $$y$$ must not be zero.

(1) $$yz<0$$ --> $$y\neq{0}$$ (II is satisfied). Don't know about $$x$$ and $$z$$. Not sufficient.

(2) $$xz>0$$ --> $$x$$ and $$z$$ are either both positive or both negative (I is satisfied). Don't know about $$y$$. Not sufficient.

(1)+(2) Both conditions are satisfied. Sufficient.

As for your doubt: we are not interested in the sign of $$z$$, we need $$x$$ and $$z$$ to be be either both positive or both negative. Next, your example is not valid: x=4, y=-1, z=-1 --> yz=4>0 and xz=-4<0 and we are given that $$yz<0$$ and $$xz>0$$.

Hope it helps.

I have a doubt; Why can't B only be true because we care for x and z signs and from II either they both are +ive or -ive and this will provide us the result.
_________________

GGG (Gym / GMAT / Girl) -- Be Serious

Its your duty to post OA afterwards; some one must be waiting for that...

Math Expert
Joined: 02 Sep 2009
Posts: 34817
Followers: 6476

Kudos [?]: 82544 [0], given: 10107

### Show Tags

30 Sep 2010, 15:36
onedayill wrote:
Bunuel wrote:
From GMAT Club Test - m25 - Q34

Inequality $$x^7*y^2*z^3>0$$ to be true:
I. $$x$$ and $$z$$ must be either both positive or both negative, AND II. $$y$$ must not be zero.

(1) $$yz<0$$ --> $$y\neq{0}$$ (II is satisfied). Don't know about $$x$$ and $$z$$. Not sufficient.

(2) $$xz>0$$ --> $$x$$ and $$z$$ are either both positive or both negative (I is satisfied). Don't know about $$y$$. Not sufficient.

(1)+(2) Both conditions are satisfied. Sufficient.

As for your doubt: we are not interested in the sign of $$z$$, we need $$x$$ and $$z$$ to be be either both positive or both negative. Next, your example is not valid: x=4, y=-1, z=-1 --> yz=4>0 and xz=-4<0 and we are given that $$yz<0$$ and $$xz>0$$.

Hope it helps.

I have a doubt; Why can't B only be true because we care for x and z signs and from II either they both are +ive or -ive and this will provide us the result.

Inequality $$x^7*y^2*z^3>0$$ to be true:
I. $$x$$ and $$z$$ must be either both positive or both negative, AND II. $$y$$ must not be zero.

So for (2): we know that $$x$$ and $$z$$ are either both positive or both negative, BUT we don't know whether $$y$$ equals to zero, because if it is then $$x^7*y^2*z^3=0$$ and not more than zero.

Hope it's clear.
_________________
Senior Manager
Joined: 25 Feb 2010
Posts: 481
Followers: 4

Kudos [?]: 79 [0], given: 10

### Show Tags

30 Sep 2010, 17:16
Bunuel wrote:
onedayill wrote:
Bunuel wrote:
From GMAT Club Test - m25 - Q34

Inequality $$x^7*y^2*z^3>0$$ to be true:
I. $$x$$ and $$z$$ must be either both positive or both negative, AND II. $$y$$ must not be zero.

(1) $$yz<0$$ --> $$y\neq{0}$$ (II is satisfied). Don't know about $$x$$ and $$z$$. Not sufficient.

(2) $$xz>0$$ --> $$x$$ and $$z$$ are either both positive or both negative (I is satisfied). Don't know about $$y$$. Not sufficient.

(1)+(2) Both conditions are satisfied. Sufficient.

As for your doubt: we are not interested in the sign of $$z$$, we need $$x$$ and $$z$$ to be be either both positive or both negative. Next, your example is not valid: x=4, y=-1, z=-1 --> yz=4>0 and xz=-4<0 and we are given that $$yz<0$$ and $$xz>0$$.

Hope it helps.

I have a doubt; Why can't B only be true because we care for x and z signs and from II either they both are +ive or -ive and this will provide us the result.

Inequality $$x^7*y^2*z^3>0$$ to be true:
I. $$x$$ and $$z$$ must be either both positive or both negative, AND II. $$y$$ must not be zero.

So for (2): we know that $$x$$ and $$z$$ are either both positive or both negative, BUT we don't know whether $$y$$ equals to zero, because if it is then $$x^7*y^2*z^3=0$$ and not more than zero.

Hope it's clear.

Sorry to say but still I didn't get this...

Why are we checking Y must not be zero?
Why can;t its be X or Z not to be zero
_________________

GGG (Gym / GMAT / Girl) -- Be Serious

Its your duty to post OA afterwards; some one must be waiting for that...

Manager
Joined: 27 Mar 2010
Posts: 125
Followers: 2

Kudos [?]: 8 [0], given: 17

### Show Tags

30 Sep 2010, 21:46
@onedayill

we need not consider if x or z is equal to zero ...

BECAUSE if you are considering only stm2 seperately then it itself says that x*z>0 that means that none of them is zero atleast.

Hope this clarifies...
Math Expert
Joined: 02 Sep 2009
Posts: 34817
Followers: 6476

Kudos [?]: 82544 [0], given: 10107

### Show Tags

30 Sep 2010, 23:40
onedayill wrote:
Sorry to say but still I didn't get this...

Why are we checking Y must not be zero?
Why can;t its be X or Z not to be zero

Statement (2) says $$xz>0$$, so neither $$x$$ nor $$z$$ equals to zero.

Check similar problems for practice:
qs-98341.html?hilit=satisfied
m21-q30-96613.html?hilit=inequality%20true%20must

Hope it helps.
_________________
Manager
Joined: 07 Feb 2010
Posts: 159
Followers: 2

Kudos [?]: 479 [0], given: 101

### Show Tags

01 Oct 2010, 04:40
from statement 1:
it depends on the value of x , x can be either positive or negative
so statement 1 not sufficient

from statement 2:
xz>0
case1: x +ve & z +ve
case 2: x -ve & z-ve
we know that y2 is +ve
so from case 1:x7y2z3= (+)(+)(+)= +
so from case 2:x7y2z3= (-)(+)(-)= +
so B alone sufficient
Math Expert
Joined: 02 Sep 2009
Posts: 34817
Followers: 6476

Kudos [?]: 82544 [0], given: 10107

### Show Tags

01 Oct 2010, 05:29
anilnandyala wrote:
from statement 1:
it depends on the value of x , x can be either positive or negative
so statement 1 not sufficient

from statement 2:
xz>0
case1: x +ve & z +ve
case 2: x -ve & z-ve
we know that y2 is +ve
so from case 1:x7y2z3= (+)(+)(+)= +
so from case 2:x7y2z3= (-)(+)(-)= +
so B alone sufficient

The red part is the reason of many mistakes on GMAT.

Square of a number is not positive, it's non-negative --> $$y^2\geq{0}$$. So for (2): we know that $$x$$ and $$z$$ are either both positive or both negative, BUT we don't know whether $$y$$ equals to zero, because if it is, then $$x^7*y^2*z^3=0$$ and not more than zero.

Hope it's clear.
_________________
Manager
Joined: 07 Feb 2010
Posts: 159
Followers: 2

Kudos [?]: 479 [0], given: 101

### Show Tags

01 Oct 2010, 07:54
Manager
Joined: 06 Nov 2009
Posts: 177
Concentration: Finance, Strategy
Followers: 1

Kudos [?]: 8 [0], given: 3

### Show Tags

01 Oct 2010, 09:53
Here the important thing is to remember that y can not be 0 if the statement is true. Therefore also statement A is needed.
SVP
Joined: 05 Jul 2006
Posts: 1515
Followers: 5

Kudos [?]: 256 [0], given: 39

is a^7 * b^2 * c^3 > 0 ? [#permalink]

### Show Tags

19 Apr 2013, 12:26
is a^7 * b^2 * c^3 >0

a) bc<0
b) ac>0
VP
Status: Far, far away!
Joined: 02 Sep 2012
Posts: 1123
Location: Italy
Concentration: Finance, Entrepreneurship
GPA: 3.8
Followers: 174

Kudos [?]: 1831 [1] , given: 219

Re: is a^7 * b^2 * c^3 > 0 ? [#permalink]

### Show Tags

19 Apr 2013, 12:32
1
KUDOS
Is $$a^7 * b^2 * c^3 >0$$

1) bc<0
2 options : +,- and -,+ but no info about a. Not sufficient

2) ac>0
2 options : +,+ and -,- but no info about b (That could equal 0 here's the trick in my opinion). Not sufficient

1+2) with 1 we know that $$b\neq{0}$$
with 2 in both cases a^8*c*3 is > 0
$$+^7*+*3>0$$
$$-^7*-^3>0$$ as well
We are not able to say so by just looking at statement 2 because $$b$$ could be $$0$$, using both statement we can discard that possibility. Sufficient
C
_________________

It is beyond a doubt that all our knowledge that begins with experience.

Kant , Critique of Pure Reason

Tips and tricks: Inequalities , Mixture | Review: MGMAT workshop
Strategy: SmartGMAT v1.0 | Questions: Verbal challenge SC I-II- CR New SC set out !! , My Quant

Rules for Posting in the Verbal Forum - Rules for Posting in the Quant Forum[/size][/color][/b]

SVP
Joined: 05 Jul 2006
Posts: 1515
Followers: 5

Kudos [?]: 256 [0], given: 39

Re: is a^7 * b^2 * c^3 > 0 ? [#permalink]

### Show Tags

19 Apr 2013, 12:35
Zarrolou wrote:
Is $$a^7 * b^2 * c^3 >0$$

1) bc<0
2 options : +,- and -,+ but no info about a. Not sufficient

2) ac>0
2 options : +,+ and -,- but no info about b (That could equal 0 here's the trick in my opinion)

1+2) with 1 we know that $$b\neq{0}$$
with 2 in both cases a^8*c*3 is > 0
$$+^7*+*3>0$$
$$-^7*-^3>0$$ as well
We are not able to say so by just looking at statement 2 because $$b$$ could be $$0$$, using both statement we can discard that possibility
C

perfect , thanks man
Math Expert
Joined: 02 Sep 2009
Posts: 34817
Followers: 6476

Kudos [?]: 82544 [0], given: 10107

Re: is a^7 * b^2 * c^3 > 0 ? [#permalink]

### Show Tags

20 Apr 2013, 04:54
yezz wrote:
is a^7 * b^2 * c^3 >0

a) bc<0
b) ac>0

Merging similar topics.
_________________
Re: is a^7 * b^2 * c^3 > 0 ?   [#permalink] 20 Apr 2013, 04:54
Similar topics Replies Last post
Similar
Topics:
3 If y > 0 is x > 0 ? 2 12 Sep 2015, 12:09
45 Is (x^7)(y^2)(z^3) > 0 ? (1) yz < 0 (2) xz > 0 28 10 Jun 2010, 12:52
6 Is (x^7)(y^2)(z^3) > 0? (m25#34) 17 06 Aug 2009, 20:55
12 Is m+z > 0? 12 15 Jul 2008, 07:55
2 Is x > 0.05? 9 23 Jun 2007, 02:50
Display posts from previous: Sort by