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

It is currently 12 Dec 2018, 20:44

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
  • 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.
  • GMATbuster's Weekly GMAT Quant Quiz, Tomorrow, Saturday at 9 AM PST

     December 14, 2018

     December 14, 2018

     09:00 AM PST

     10:00 AM PST

    10 Questions will be posted on the forum and we will post a reply in this Topic with a link to each question. There are prizes for the winners.

x ≠ 0. Is x^2>x^4?

  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: 6625
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post 10 Aug 2018, 01:33
1
3
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

66% (00:49) correct 34% (01:43) wrong based on 80 sessions

HideShow timer Statistics

[Math Revolution GMAT math practice question]

\(x ≠ 0\). Is \(x^2>x^4?\)

\(1) x^2<1\)
\(2) x^2<2x\)

_________________

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"

Director
Director
User avatar
P
Status: Learning stage
Joined: 01 Oct 2017
Posts: 931
WE: Supply Chain Management (Energy and Utilities)
Premium Member
Re: x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post 10 Aug 2018, 04:28
2
MathRevolution wrote:
[Math Revolution GMAT math practice question]

\(x ≠ 0\). Is \(x^2>x^4?\)

\(1) x^2<1\)
\(2) x^2<2x\)


Re-phrasing question stem:-
\(x^2>x^4\)
Or, \(x^4-x^2<0\)
Or, \(x^2\left(x+1\right)\left(x-1\right)<0\)
-1<x<0 or 0<x<1


St1:- \(x^2<\)
Or, x^2-1<0
Or, (x+1)(x-1)<0
-1<x<1
Since \(x\neq{0}\), hence -1<x<0 or 0<x<1

Sufficient.

St2:- \(x^2<2x\)
Or, x(x-2)<0
So, 0<x<2
Insufficient.

Ans. (A)
_________________

Regards,

PKN

Rise above the storm, you will find the sunshine

VP
VP
User avatar
D
Joined: 09 Mar 2016
Posts: 1215
x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post Updated on: 13 Aug 2018, 05:54
PKN wrote:
MathRevolution wrote:
[Math Revolution GMAT math practice question]

\(x ≠ 0\). Is \(x^2>x^4?\)

\(1) x^2<1\)
\(2) x^2<2x\)


Re-phrasing question stem:-
\(x^2>x^4\)
Or, \(x^4-x^2<0\)
Or, \(x^2\left(x+1\right)\left(x-1\right)<0\)
-1<x<0 or 0<x<1


St1:- \(x^2<\)
Or, x^2-1<0
Or, (x+1)(x-1)<0
-1<x<1
Since \(x\neq{0}\), hence -1<x<0 or 0<x<1

Sufficient.

St2:- \(x^2<2x\)
Or, x(x-2)<0
So, 0<x<2
Insufficient.

Ans. (A)



hi PKN

hope my questions find you well :)

is it necessary to rephrase this question to solve it ? looking at initial form of both statements, i thought correct answer was E because in both cases we have even roots that yield both negative and positive values :? why

Also, why you changed inequality sign here \(x^4-x^2<0\) :? We didn't divide by or multiply with negative value, did we ?

And one more question I understand what factoring out is but want to doublecheck it with you :-)

hey gmatbusters when you get the chance can you please answer my questions above :-) many thanks in advance!

Or, \(x^4-x^2<0\)
Or, \(x^2\left(x+1\right)\left(x-1\right)<0\)


\(x^4-x^2<0\) from here i factor out \(x^2\) and get \(x^2(x^2-1)\) is it correct than I apply this formula \(a^2-b^2= (a+b)(a-b)\) is my understanding correct ?

many thanks for taking time to explain :)

Originally posted by dave13 on 12 Aug 2018, 01:32.
Last edited by dave13 on 13 Aug 2018, 05:54, edited 1 time in total.
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6625
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post 13 Aug 2018, 05:24
1
=>

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.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

\(x^2>x^4\)
\(=> x^4 - x^2 < 0\)
\(=> x^2 ( x^2 – 1 ) < 0\)
\(=> ( x^2 – 1 ) < 0\)
\(=> ( x + 1 )( x – 1 ) < 0\)
\(=> -1 < x < 1\)

This is equivalent to condition 1).
Thus, condition 1) is sufficient.

Condition 2)
\(x^2<2x\)
\(=> x^2 - 2x < 0\)
\(=> x(x – 2) < 0\)
\(=> 0 < x < 2\)

In inequality questions, the law “Question is King” tells us that if the solution set of the question includes the solution set of the condition, then the condition is sufficient
However, the solution set of the question -1 < x < 1 does not include the solution set of the condition, 0 < x < 2. Thus, condition 2) is not sufficient.


Therefore, A is the answer.
_________________

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"

Senior DS Moderator
User avatar
V
Joined: 27 Oct 2017
Posts: 1118
Location: India
Concentration: International Business, General Management
GPA: 3.64
WE: Business Development (Energy and Utilities)
Premium Member CAT Tests
Re: x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post 13 Aug 2018, 06:04
1
@dace13

Please find my response in GREEN

[/quote]


hi PKN

hope my questions find you well :)

is it necessary to rephrase this question to solve it ?- REPHRASING THE QUESTION MAKES IT EASIER
looking at initial form of both statements, i thought correct answer was E because in both cases we have even roots that yield both negative and positive values :? why

Also, why you changed inequality sign here \(x^4-x^2<0\) :? - THIS IS BECAUSE THE TERMS ARE TAKEN TO THE OTHER SIDE OF INEQUALITY.
We didn't divide by or multiply with negative value, did we ?- MULTIPLY BY (-)1 IS SAME AS TAKING THE TERMS TO OTHER SIDE OF INEQUALITY. BOTH ARE EQUIVALENT.
And one more question I understand what factoring out is but want to doublecheck it with you :-)

hey gmatbusters when you get the chance can you please answer my questions above :-) many thanks in advance!

Or, \(x^4-x^2<0\)
Or, \(x^2\left(x+1\right)\left(x-1\right)<0\)


\(x^4-x^2<0\) from here i factor out \(x^2\) and get \(x^2(x^2-1)\) is it correct than I apply this formula \(a^2-b^2= (a+b)(a-b)\) is my understanding correct ?- YOUR UNDERSTANDING IS CORRECT

many thanks for taking time to explain :)[/quote]
_________________

Win GMAT CLUB Test- Weekly Quant Quiz Contest
Weekly Quant Quiz Questions- Direct Download
SC: Confusable words

All you need for Quant, GMAT PS Question Directory,GMAT DS Question Directory
Error log/Key Concepts
Combination Concept: Division into groups
Question of the Day (QOTD)
Free GMAT CATS

VP
VP
User avatar
D
Joined: 09 Mar 2016
Posts: 1215
x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post Updated on: 13 Aug 2018, 06:52
gmatbusters many thanks for your prompt and helpful reply :) one question regarding flipping signs if you say we flip the sign when we take one term to other side, then in my example below should i change inequility sign ?

\(x+5>8\)

\(x<8-5\) (here i flipped sign because i took one term to the other side)

\(x<3\)

is it correct ? if not why ?

Originally posted by dave13 on 13 Aug 2018, 06:42.
Last edited by dave13 on 13 Aug 2018, 06:52, edited 1 time in total.
VP
VP
User avatar
D
Joined: 09 Mar 2016
Posts: 1215
x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post 13 Aug 2018, 06:49
MathRevolution wrote:
=>

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.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

\(x^2>x^4\)
\(=> x^4 - x^2 < 0\)
\(=> x^2 ( x^2 – 1 ) < 0\)
\(=> ( x^2 – 1 ) < 0\)
\(=> ( x + 1 )( x – 1 ) < 0\)
\(=> -1 < x < 1\)

This is equivalent to condition 1).
Thus, condition 1) is sufficient.

Condition 2)
\(x^2<2x\)
\(=> x^2 - 2x < 0\)
\(=> x(x – 2) < 0\)
\(=> 0 < x < 2\)

In inequality questions, the law “Question is King” tells us that if the solution set of the question includes the solution set of the condition, then the condition is sufficient
However, the solution set of the question -1 < x < 1 does not include the solution set of the condition, 0 < x < 2. Thus, condition 2) is not sufficient.


Therefore, A is the answer.




MathRevolution, Greetings Revolutioner :)

you say " Forget conventional ways of solving math questions" but you are using pure conventonal algebraic method to solve question (step by step), arent you? :?
VP
VP
User avatar
D
Joined: 09 Mar 2016
Posts: 1215
Re: x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post 13 Aug 2018, 07:15
MathRevolution wrote:
=>

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.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

\(x^2>x^4\)
\(=> x^4 - x^2 < 0\)
\(=> x^2 ( x^2 – 1 ) < 0\)
\(=> ( x^2 – 1 ) < 0\)
\(=> ( x + 1 )( x – 1 ) < 0\)
\(=> -1 < x < 1\)

This is equivalent to condition 1).
Thus, condition 1) is sufficient.

Condition 2)
\(x^2<2x\)
\(=> x^2 - 2x < 0\)
\(=> x(x – 2) < 0\)
\(=> 0 < x < 2\)

In inequality questions, the law “Question is King” tells us that if the solution set of the question includes the solution set of the condition, then the condition is sufficient
However, the solution set of the question -1 < x < 1 does not include the solution set of the condition, 0 < x < 2. Thus, condition 2) is not sufficient.


Therefore, A is the answer.


gmatbusters have a look at highlighted part. the inequility sign was NOT FLIPPED WHEN THE TERM WAS TAKEN TO THE OTHER SIDE. it contradicts your explanation :? can you provide detailed explanation please :-)
Senior DS Moderator
User avatar
V
Joined: 27 Oct 2017
Posts: 1118
Location: India
Concentration: International Business, General Management
GPA: 3.64
WE: Business Development (Energy and Utilities)
Premium Member CAT Tests
Re: x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post 13 Aug 2018, 07:27
1
You didn't understand it correctly,

You need not flip it while taking the variable on the other side
See, x+5>8
Now if we take x on other side, 5-8>-x, or -3>-x

Now, the pointed part of the inequality is towards x earlier it was open part of the inequality sign.

1) To find x we can either multiply the inequality by (-)1 , we get 3<x ( flip the inequality while multiplying or dividing by negative)

other approach

2) swap the x on other side to make it positive (no flipping of inequality sign is required now)
x>3






dave13 wrote:
gmatbusters many thanks for your prompt and helpful reply :) one question regarding flipping signs if you say we flip the sign when we take one term to other side, then in my example below should i change inequility sign ?

\(x+5>8\)

\(x<8-5\) (here i flipped sign because i took one term to the other side)- INEQUALITY IS NOT TO BE FLIPPED

\(x<3\)

is it correct ? if not why ?

_________________

Win GMAT CLUB Test- Weekly Quant Quiz Contest
Weekly Quant Quiz Questions- Direct Download
SC: Confusable words

All you need for Quant, GMAT PS Question Directory,GMAT DS Question Directory
Error log/Key Concepts
Combination Concept: Division into groups
Question of the Day (QOTD)
Free GMAT CATS

Senior DS Moderator
User avatar
V
Joined: 27 Oct 2017
Posts: 1118
Location: India
Concentration: International Business, General Management
GPA: 3.64
WE: Business Development (Energy and Utilities)
Premium Member CAT Tests
Re: x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post 13 Aug 2018, 07:34
1
1) Flip the inequality sign if multiply or divide by a negative
2)when you take the variable to other side, the Flipping of inequality sign not required.


See if 2-x > 3 ....(eq1)
taking variable on the side side, -1>x ....(eq2) ( i didn't flip the sign)
BUT , We generally write the variable on left, S
o the final inequality is x<-1... (eq3)

eq 2 & eq3 are same, but it seems that inequality sign has been flipped , actually it is not flipped.


dave13 wrote:
MathRevolution wrote:
=>

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.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

\(x^2>x^4\)
\(=> x^4 - x^2 < 0\)
\(=> x^2 ( x^2 – 1 ) < 0\)
\(=> ( x^2 – 1 ) < 0\)
\(=> ( x + 1 )( x – 1 ) < 0\)
\(=> -1 < x < 1\)

This is equivalent to condition 1).
Thus, condition 1) is sufficient.

Condition 2)
\(x^2<2x\)
\(=> x^2 - 2x < 0\)
\(=> x(x – 2) < 0\)
\(=> 0 < x < 2\)

In inequality questions, the law “Question is King” tells us that if the solution set of the question includes the solution set of the condition, then the condition is sufficient
However, the solution set of the question -1 < x < 1 does not include the solution set of the condition, 0 < x < 2. Thus, condition 2) is not sufficient.


Therefore, A is the answer.


gmatbusters have a look at highlighted part. the inequility sign was NOT FLIPPED WHEN THE TERM WAS TAKEN TO THE OTHER SIDE. it contradicts your explanation :?

1) Flip the inequality sign if multiply or divide by a negative
2)when you take the variable to other side, the Flipping of inequality sign not required.

can you provide detailed explanation please :-)

_________________

Win GMAT CLUB Test- Weekly Quant Quiz Contest
Weekly Quant Quiz Questions- Direct Download
SC: Confusable words

All you need for Quant, GMAT PS Question Directory,GMAT DS Question Directory
Error log/Key Concepts
Combination Concept: Division into groups
Question of the Day (QOTD)
Free GMAT CATS

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6625
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: x ≠ 0. Is x^2>x^4?  [#permalink]

Show Tags

New post 15 Aug 2018, 22:41
1
dave13 wrote:
MathRevolution wrote:
=>

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.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

\(x^2>x^4\)
\(=> x^4 - x^2 < 0\)
\(=> x^2 ( x^2 – 1 ) < 0\)
\(=> ( x^2 – 1 ) < 0\)
\(=> ( x + 1 )( x – 1 ) < 0\)
\(=> -1 < x < 1\)

This is equivalent to condition 1).
Thus, condition 1) is sufficient.

Condition 2)
\(x^2<2x\)
\(=> x^2 - 2x < 0\)
\(=> x(x – 2) < 0\)
\(=> 0 < x < 2\)

In inequality questions, the law “Question is King” tells us that if the solution set of the question includes the solution set of the condition, then the condition is sufficient
However, the solution set of the question -1 < x < 1 does not include the solution set of the condition, 0 < x < 2. Thus, condition 2) is not sufficient.


Therefore, A is the answer.




MathRevolution, Greetings Revolutioner :)

you say " Forget conventional ways of solving math questions" but you are using pure conventonal algebraic method to solve question (step by step), arent you? :?


The mentioned "conventional way" means checking condition 1), condition 2) and both conditions together and so on. It takes too much time.
The first step of VA method of Math Revolution is modifying a original condition and a question. By that step, 30% of questions can be solved.
When we modify them, we should use algebraic method, of course.
_________________

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: x ≠ 0. Is x^2>x^4? &nbs [#permalink] 15 Aug 2018, 22:41
Display posts from previous: Sort by

x ≠ 0. Is x^2>x^4?

  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®.