GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 11 Dec 2018, 22:10

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.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
  • Free GMAT Prep Hour

     December 11, 2018

     December 11, 2018

     09:00 PM EST

     10:00 PM EST

    Strategies and techniques for approaching featured GMAT topics. December 11 at 9 PM EST.
  • The winning strategy for 700+ on the GMAT

     December 13, 2018

     December 13, 2018

     08:00 AM PST

     09:00 AM PST

    What people who reach the high 700's do differently? We're going to share insights, tips and strategies from data we collected on over 50,000 students who used examPAL.

Is x < 0? 1) x^5+x^3+1<0

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6621
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Is x < 0? 1) x^5+x^3+1<0  [#permalink]

Show Tags

New post 14 Nov 2017, 00:12
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

86% (01:00) correct 14% (01:50) wrong based on 57 sessions

HideShow timer Statistics

[GMAT math practice question]

Is \(x < 0\)?

1) \(x^5+x^3+1<0\)
2) \(x^3+1 < 0\)

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Expert
User avatar
V
Joined: 02 Aug 2009
Posts: 7102
Re: Is x < 0? 1) x^5+x^3+1<0  [#permalink]

Show Tags

New post 14 Nov 2017, 01:11
MathRevolution wrote:
[GMAT math practice question]

Is \(x < 0\)?

1) \(x^5+x^3+1<0\)
2) \(x^3+1 < 0\)



1) \(x^5+x^3+1<0\)..
\(x^5+x^3+1<0......x^3(x^2+1)+1<0.......x^3(x^2+1)<-1\)
\(x^2+1\) is POSITIVE, so \(x^3\) has to be NEGATIVE
suff

2) \(x^3+1 < 0\)..
\(x^3+1 < 0......x^3<-1.....x<-1\), so x<0
suff

D
_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


GMAT online Tutor

Manager
Manager
avatar
S
Joined: 11 Oct 2016
Posts: 73
Location: India
GMAT 1: 610 Q47 V28
GMAT ToolKit User
Re: Is x < 0? 1) x^5+x^3+1<0  [#permalink]

Show Tags

New post 14 Nov 2017, 19:32
IMO B

X^3 (X^2+1) < -1
X should be less than -1

X^3 < -1
X should be less than -1
_________________

Hit kudos if you like my post

Today's preparation determines tomorrow's achievement.

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6621
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Is x < 0? 1) x^5+x^3+1<0  [#permalink]

Show Tags

New post 16 Nov 2017, 00:15
=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

Since the question includes 1 variable (x) and 0 equations, D is most likely to be the answer.

Condition 1)
\(x^5+x^3+1<0\) implies that \(x^3(x^2+1)< -1\).
Since \(x^2+1>0\) always, \(x^3< \frac{-1}{x^2+1}<0\).
Therefore, \(x<0.\)
This is sufficient.

Condition 2)
\(x^3+1 < 0\) is equivalent to \((x+1)(x^2-x+1)<0\). Since
\(x^2-x+1>0\) always, it follows that \(x+1<0\).
This is sufficient, too.

Therefore, the answer is D, as expected.


If the original condition includes “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations” etc., one more equation is required to answer the question. If each of conditions 1) and 2) provide an additional equation, there is a 59 % chance that D is the answer, a 38% chance that A or B is the answer, and a 3% chance that the answer is C or E. Thus, answer D (conditions 1) and 2), when applied separately, are sufficient to answer the question) is most likely, but there may be cases where the answer is A,B,C or E.
Answer: D
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

GMAT Club Bot
Re: Is x < 0? 1) x^5+x^3+1<0 &nbs [#permalink] 16 Nov 2017, 00:15
Display posts from previous: Sort by

Is x < 0? 1) x^5+x^3+1<0

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.