Last visit was: 10 Jul 2025, 20:25 It is currently 10 Jul 2025, 20:25
Home
GMAT
Messages
Tests
Schools
Events
Rewards
Chat
My Profile
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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
User avatar
ninomoi
User avatar
Joined: 09 Sep 2004
Last visit: 21 May 2007
Posts: 95
Own Kudos:
27
 [11]
Posts: 95
Kudos: 27
 [11]
If n is an integer, is -3x^n positive? Updated on: 08 Oct 2016, 02:57
Originally posted by ninomoi on 15 May 2007, 02:03.
Last edited by Bunuel on 08 Oct 2016, 02:57, edited 2 times in total.
Renamed the topic and edited the question.
3
Kudos
Add Kudos
8
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

15% (low)

Question Stats:

79% (00:57) correct 21% (00:56) wrong based on 556 sessions

History

Date
Time
Result
Not Attempted Yet
If n is an integer, is \(-3x^n\) positive?

(1) x is negative.
(2) n is odd.
ShowHide Answer
Official Answer
C
User avatar
Sergey_is_cool
User avatar
Joined: 03 May 2007
Last visit: 04 Jan 2011
Posts: 141
Own Kudos:
20
 [1]
Posts: 141
Kudos: 20
 [1]
If n is an integer, is -3x^n positive? 15 May 2007, 07:52
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
ninomoi
If n is an integer, is -3x^n positive?

1. x is negative
2. n is odd

pls explain. Thanks


Answer is C

in order for the expression to be positive we have to have x negative (-*-=+)
but we also know that x^n where n is even will give us positive number
-2^2=-2*-2=4 so we have to have n odd
avatar
gmatready7
avatar
Joined: 29 Mar 2010
Last visit: 08 Apr 2011
Posts: 18
Own Kudos:
2
Posts: 18
Kudos: 2
If n is an integer, is -3x^n positive? 29 Mar 2010, 13:58
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Gmat Prep says the answer is C, but I think it is A. Can someone tell me what I am doing wrong?

1. x is negative

So, let x be -1.
1 ^ 2 * - * -3 = 3
1 ^ 3 * - * -3 = 3

If x is negative the answer is always positive. If the problem were -3(x)^n then that answer would be C. However, without the brackets you must distribute the negative after you take x^n...therefore the answer will always be a negative number multiplied by -3 which gives a positive answer.
avatar
PeterFaulkner
avatar
Joined: 19 Feb 2010
Last visit: 12 Aug 2010
Posts: 1
Posts: 1
Kudos: 0
If n is an integer, is -3x^n positive? 01 Apr 2010, 13:01
Kudos
Add Kudos
Bookmarks
Bookmark this Post
gmatready7
Gmat Prep says the answer is C, but I think it is A. Can someone

If x is negative the answer is always positive. If the problem were -3(x)^n then that answer would be C. However, without the brackets you must distribute the negative after you take x^n...therefore the answer will always be a negative number multiplied by -3 which gives a positive answer.


I think it's an issue of order of operations. Exponents come before multiplication so if x = -1 and n is even say 2
Then -3 * -1^2 = -3 * 1 = -3

x = -1 and n is odd say 3
then -3 * -1^3 = -3 * -1 = 3

so A by itself is insufficient....
Please correct me if I am wrong
avatar
gmatready7
avatar
Joined: 29 Mar 2010
Last visit: 08 Apr 2011
Posts: 18
Own Kudos:
2
Posts: 18
Kudos: 2
If n is an integer, is -3x^n positive? 01 Apr 2010, 14:00
Kudos
Add Kudos
Bookmarks
Bookmark this Post
PeterFaulkner
gmatready7
Gmat Prep says the answer is C, but I think it is A. Can someone

If x is negative the answer is always positive. If the problem were -3(x)^n then that answer would be C. However, without the brackets you must distribute the negative after you take x^n...therefore the answer will always be a negative number multiplied by -3 which gives a positive answer.


I think it's an issue of order of operations. Exponents come before multiplication so if x = -1 and n is even say 2
Then -3 * -1^2 = -3 * 1 = -3

x = -1 and n is odd say 3
then -3 * -1^3 = -3 * -1 = 3

so A by itself is insufficient....
Please correct me if I am wrong
But you can raise a negative number to an even power and the answer is still negative. -1^2 = -1. For it to be positive you must use brackets around the -1....(-1)^2 = 1. This is why I chose answer a. Are we to assume there are brackets on the GMAT even though they are not shown?
User avatar
chetan2u
User avatar
GMAT Expert
Joined: 02 Aug 2009
Last visit: 10 Jul 2025
Posts: 11,294
Own Kudos:
41,667
Given Kudos: 333
Status:Math and DI Expert
Products:
My Reviews
Expert
Expert reply
Posts: 11,294
Kudos: 41,667
If n is an integer, is -3x^n positive? 11 Jan 2016, 21:23
Kudos
Add Kudos
Bookmarks
Bookmark this Post
NoHalfMeasures
If n is an integer, is -3x^n positive?
(1) x is negative.
(2) n is odd.

pls press kudos if you liked the question

Hi,
what does the sign of -3x^n depends on ...
1) sign of x..
2) value(odd/even) of n, and not on sign of n, as it will turn the x variable in a fraction but will not effect the sign of that fraction or integer..

lets see the statements..
(1) x is negative.
we are told of one of the two things required .. insuff

(2) n is odd.
we are told of one of the two things required .. insuff

combined both the info is provided ... suff
User avatar
lpetroski
User avatar
Joined: 30 Dec 2015
Last visit: 07 Oct 2019
Posts: 179
Own Kudos:
833
Given Kudos: 99
Location: United States
Concentration: Strategy, Organizational Behavior
Schools: Judge"18 (WD) LBS '19 (A) INSEAD Jan'18 (M)
GPA: 3.88
WE:Business Development (Hospitality and Tourism)
Products:
My Reviews
Schools: Judge"18 (WD) LBS '19 (A) INSEAD Jan'18 (M)
Posts: 179
Kudos: 833
If n is an integer, is -3x^n positive? 17 Jan 2016, 06:51
Kudos
Add Kudos
Bookmarks
Bookmark this Post
chetan2u
NoHalfMeasures
If n is an integer, is -3x^n positive?
(1) x is negative.
(2) n is odd.

pls press kudos if you liked the question

Hi,
what does the sign of -3x^n depends on ...
1) sign of x..
2) value(odd/even) of n, and not on sign of n, as it will turn the x variable in a fraction but will not effect the sign of that fraction or integer..

lets see the statements..
(1) x is negative.
we are told of one of the two things required .. insuff

(2) n is odd.
we are told of one of the two things required .. insuff

combined both the info is provided ... suff

I don't understand -- if x is negative then -3(x) = positive number and -3x^n will be positive -- is it for PEMDAS?

That x^n operation must come first?
User avatar
chetan2u
User avatar
GMAT Expert
Joined: 02 Aug 2009
Last visit: 10 Jul 2025
Posts: 11,294
Own Kudos:
41,667
Given Kudos: 333
Status:Math and DI Expert
Products:
My Reviews
Expert
Expert reply
Posts: 11,294
Kudos: 41,667
If n is an integer, is -3x^n positive? 17 Jan 2016, 07:02
Kudos
Add Kudos
Bookmarks
Bookmark this Post
lpetroski
chetan2u
NoHalfMeasures
If n is an integer, is -3x^n positive?
(1) x is negative.
(2) n is odd.

pls press kudos if you liked the question

Hi,
what does the sign of -3x^n depends on ...
1) sign of x..
2) value(odd/even) of n, and not on sign of n, as it will turn the x variable in a fraction but will not effect the sign of that fraction or integer..

lets see the statements..
(1) x is negative.
we are told of one of the two things required .. insuff

(2) n is odd.
we are told of one of the two things required .. insuff

combined both the info is provided ... suff

I don't understand -- if x is negative then -3(x) = positive number and -3x^n will be positive -- is it for PEMDAS?

That x^n operation must come first?

Hi,
x^n operation is not there in PEMDAS..
because x^n is one number..
example 4=2^2 so if we have 7*2^2, it means 7*4, because 2^2 is one number..
same goes for x^n..
hence even sign of n is important..
because power of an even number will make any number positive, even if it is negative..
say x=-2 and n=2..
(-2)^2=-2*-2=4, whereas -2^3=-2*-2*-2=-8, a -ive number..
hope it helps
avatar
gthrb22
avatar
Joined: 11 Aug 2016
Last visit: 30 Jul 2020
Posts: 17
Own Kudos:
1
Given Kudos: 3
Schools: Alberta University Rotman '17 Sauder 'Dec 18
Schools: Alberta University Rotman '17 Sauder 'Dec 18
Posts: 17
Kudos: 1
If n is an integer, is -3x^n positive? 07 Oct 2016, 22:01
Kudos
Add Kudos
Bookmarks
Bookmark this Post
ninomoi
If n is an integer, is -3x^n positive?

1. x is negative
2. n is odd

pls explain. Thanks

Answer should be C

For the given statement to be positive x should be negative and n should be odd number
St 1 :
states that x is negative but we dont know if n is even or odd if n is even insuff if n is odd sufficient so st 1 is insuff
St 2:
States that n is odd again we dont know the value of x whether positive or negative if positive answer to question is no if negative answer to ques is yes again insuff

Combined sufficient since n is odd and x is negative statement will be positive.
User avatar
AkshdeepS
User avatar
Joined: 13 Apr 2013
Last visit: 10 Jul 2025
Posts: 1,441
Own Kudos:
1,823
Given Kudos: 1,001
Status:It's near - I can see.
Location: India
Concentration: International Business, Operations
GPA: 3.01
WE:Engineering (Real Estate)
Products:
My Reviews
Posts: 1,441
Kudos: 1,823
If n is an integer, is -3x^n positive? 21 Mar 2018, 06:04
Kudos
Add Kudos
Bookmarks
Bookmark this Post
ninomoi
If n is an integer, is \(-3x^n\) positive?

(1) x is negative.
(2) n is odd.

Given: n = Integer

Question : \(-3x^n\) > 0 ?

Or, Is -3 * x^n > 0 ?

Or, Is x^n > 0 ?

St 1: x < 0, but we don't know whether "n" is even or odd.

If "n" is even the answer to the question is YES

If "n" is odd the answer to the question is NO (Insufficient)

St 2: n is odd, we don't know "x" is positive or negative.

If "x" is positive the answer to the question is YES

If "x" is negative the answer to the question is NO (Insufficient)

Combining both statements we get,

x is -ve and n is odd, therefore we can say that x^n < 0 always.

Answer to the question is "NO"

Sufficient (C)
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 37,380
Own Kudos:
1,010
Posts: 37,380
Kudos: 1,010
If n is an integer, is -3x^n positive? 27 Mar 2025, 09:54
Kudos
Add Kudos
Bookmarks
Bookmark this Post
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.
Moderator:
Bunuel
Math Expert
102631 posts