NEW HERE? LEARN MORE
closeclose
It is currently 27 Sep 2023, 18:46
Register
GMAT Club Tests
Decision Tracker
My Rewards
New posts
New comers' posts

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

If n is an integer, is -3x^n positive?

11 posts Go to First Unread Post
Print view
NEW TOPIC
POST REPLY
Downloads
My Bookmarks
Reviews
SORT BY:
Date
Kudos
User avatar
ninomoi
Manager
Manager
Joined: 09 Sep 2004
Posts: 96
If n is an integer, is -3x^n positive? [#permalink] New post  Updated on: 08 Oct 2016, 02:57
3
Kudos
6
Bookmarks
Quiz Dashboard Attempt only this question Same topic and source Same topic and difficulty Same source and difficulty Random Chronological Reverse chronological Learn more
00:00
A
B
C
D
E

Difficulty:

15% (low)

Question Stats:

79% (00:56) correct 21% (00:59) wrong based on 454 sessions

Hide Show timer Statistics

If n is an integer, is \(-3x^n\) positive?

(1) x is negative.
(2) n is odd.
ShowHide Answer
Official Answer
Official Answer and Stats are available only to registered users. Register/Login.

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.
Quiz Dashboard Attempt only this question Same topic and source Same topic and difficulty Same source and difficulty Random Chronological Reverse chronological Learn more
User avatar
Sergey_is_cool
Manager
Manager
Joined: 03 May 2007
Posts: 141
Re: If n is an integer, is -3x^n positive? [#permalink] New post  15 May 2007, 07:52
1
Kudos
ninomoi wrote:
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
Intern
Intern
Joined: 29 Mar 2010
Posts: 18
Re: If n is an integer, is -3x^n positive? [#permalink] New post  29 Mar 2010, 13:58
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
Intern
Intern
Joined: 19 Feb 2010
Posts: 1
Re: If n is an integer, is -3x^n positive? [#permalink] New post  01 Apr 2010, 13:01
gmatready7 wrote:
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
Intern
Intern
Joined: 29 Mar 2010
Posts: 18
Re: If n is an integer, is -3x^n positive? [#permalink] New post  01 Apr 2010, 14:00
PeterFaulkner wrote:
gmatready7 wrote:
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
L
chetan2u
Math Expert
Joined: 02 Aug 2009
Posts: 10391
Reviews Badge
Re: If n is an integer, is -3x^n positive? [#permalink] New post  11 Jan 2016, 21:23
Expert Reply
NoHalfMeasures wrote:
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
_________________
1. Absolute modulus:. 2. Fractions: 3. Percentage increase: 4. Combinations:
Signature Read More
avatar
S
lpetroski
Manager
Manager
Joined: 30 Dec 2015
Posts: 181
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)
Reviews Badge
Re: If n is an integer, is -3x^n positive? [#permalink] New post  17 Jan 2016, 06:51
chetan2u wrote:
NoHalfMeasures wrote:
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
L
chetan2u
Math Expert
Joined: 02 Aug 2009
Posts: 10391
Reviews Badge
Re: If n is an integer, is -3x^n positive? [#permalink] New post  17 Jan 2016, 07:02
Expert Reply
lpetroski wrote:
chetan2u wrote:
NoHalfMeasures wrote:
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
_________________
1. Absolute modulus:. 2. Fractions: 3. Percentage increase: 4. Combinations:
Signature Read More
avatar
gthrb22
Intern
Intern
Joined: 11 Aug 2016
Posts: 17
Schools: Alberta University Rotman '17 Sauder 'Dec 18
Re: If n is an integer, is -3x^n positive? [#permalink] New post  07 Oct 2016, 22:01
ninomoi wrote:
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
L
AkshdeepS
SVP
SVP
Joined: 13 Apr 2013
Status:It's near - I can see.
Posts: 1504
Location: India
Concentration: International Business, Operations
GPA: 3.01
WE:Engineering (Real Estate)
Reviews Badge
If n is an integer, is -3x^n positive? [#permalink] New post  21 Mar 2018, 06:04
ninomoi wrote:
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)
_________________
"Do not watch clock; Do what it does. KEEP GOING."
Signature Read More
User avatar
bumpbot
Non-Human User
Joined: 09 Sep 2013
Posts: 29502
Re: If n is an integer, is -3x^n positive? [#permalink] New post  28 Mar 2023, 04:31
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.
_________________
GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources
Signature Read More
GMAT Club Bot
gmatclubot
Re: If n is an integer, is -3x^n positive? [#permalink]
28 Mar 2023, 04:31
NEW TOPIC
POST REPLY
Downloads
My Bookmarks
Reviews
Moderator:
Bunuel
Math Expert
89492 posts

cron

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions