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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Is \(x>x^3\)? --> is \(x^3-x<0\)? --> is \((x+1)x(x-1)<0\)? is \(x<-1\) or \(0<x<1\)

(1) x<0. Not sufficient.

(2) x^2-x^3>2 --> \(x^2(1-x)>2\) --> only true for \(x<-1\) (note that if \(x>1\) then \(x^2(1-x)\) is negative so this range is not good and if \(-1\leq{x}\leq{1}\) then \(x^2(1-x)\leq{2}\) so this range is also not good). Sufficient.

I goofed on this because I tricked myself but this is easy...think about it as always before putting pen to paper.. When is x>x^3? ONLY when x = negative integer OR a positive fraction. 1) x= -ve, ok but is it a fraction? Insuff 2) x^2 - x^3 >2 x^2 (x-1)<2 Use gurpreets method to draw the number line. You will see that Statement is positive for all: x>1 = positive, x>0 = positive Therefore between 0 and 1 the statement is negative..hence the original statement holds true. Because X is a positive fraction, B is sufficient.

(2) x^2-x^3>2 --> \(x^2(1-x)>2\) --> only true for \(x<-1\) (note that if \(x>1\) then \(x^2(1-x)\) is negative so this range is not good and if \(-1\leq{x}\leq{1}\) then \(x^2(1-x)\leq{2}\) so this range is also not good). Sufficient.

Answer: B.

Hi Bunuel,

For x^2-x^3>2 how did you directly arrive at the intervals <-1 between -1 and 1 and >1. When we deal with (1-x) >2 we get x <-1. But how did you chose the other point 1?

(2) x^2-x^3>2 --> \(x^2(1-x)>2\) --> only true for \(x<-1\) (note that if \(x>1\) then \(x^2(1-x)\) is negative so this range is not good and if \(-1\leq{x}\leq{1}\) then \(x^2(1-x)\leq{2}\) so this range is also not good). Sufficient.

Answer: B.

Hi Bunuel,

For x^2-x^3>2 how did you directly arrive at the intervals <-1 between -1 and 1 and >1. When we deal with (1-x) >2 we get x <-1. But how did you chose the other point 1?

Hi Bunuel, Thanks for your reply and reference to some wonderful materials around quadratic inequalities.

May I ask you one more question - going back to the basics now. What would be the roots of the eqn we have in hand in this post: x^2 - x^3 >2. I solved the roots to be 0 and -1 by following the below steps: x^2(1-x)>2 X^2 implies 0 is a root. 1-x>2 implies x<-1, so -1 is a root. From your explanations the roots seem to be 1 and -1. Where am I going wrong? (I also saw another post of yours where I was not able to solve the correct roost when x^3 was involved. Please help.)

Last edited by Jaisri on 07 Mar 2013, 06:28, edited 1 time in total.

Nothing to add after Bunuel's explanation. But just writing down how to get the inequality x<-1 from F.S 2 for those who couldn't get it.

F.S 1 clearly not sufficient. Take x= -1,you get a NO for stem, but for -0.5, you get a YES.

F.S 2, states \(x^2-x^3-2>\)0

or\(( x^2-1)-(x^3-1)>0\)

or\((x-1)[(x+1) - (x^2+1+x)]>0\)

or\((x-1)(-x^2)\)>0. Thus, (x-1) has to be negative

or x-1<0

or x<-1.

Sufficient.

B.

+1 Kudos. Thanks for showing how to solve this inequality! There is a minor change though... x-1 >0 gives x<1 and not x <-1. Bunuel seems to have considered -1 and 1 as the roots. Any reasons for that?

+1 Kudos. Thanks for showing how to solve this inequality! There is a minor change though... x-1 >0 gives x<1 and not x <-1. Bunuel seems to have considered -1 and 1 as the roots. Any reasons for that?

thanks for pointing out the mistake. It was a splendidly foolish mistake. Apologies.
_________________

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.
_________________

You can either use inequalities here or the big picture approach.

When is x greater than x^3? It is when x < -1 or 0 < x <1. (Recall that we should know the relations of x, x^2 and x^3 in the ranges 'less than -1', '-1 to 0', '0 to 1' and 'greater than 1')

(1) x < 0 When x is between -1 and 0, x^3 is greater than x. When x < -1, then x is greater than x^3. So this statement alone is not sufficient.

(2) x^2 - x^3 > 2 Now, this is not very easy to handle using inequalities. Without the cube, we would have just taken 2 to the other side and solved the quadratic. But this will be more easily solved using the big picture. Think of a number line. What does x^2 - x^3 > 2 imply? It means x^2 is greater than x^3 and is 2 units to the right of x^3 on the number line. x^2 is never negative so it must be to the right of 0. Now there are two cases: Either x^2 is between 0 and 1 or it is greater than 1. If x^2 were between 0 and 1, x would be between -1 and 1 and x^3 would be between 0 and -1. In this case, difference between x^3 and x^2 cannot be greater than 2. Hence this is not possible. So x^2 must be to the right of 1 and hence, x would be greater than 1 or less than -1. If x were greater than 1, x^3 would be greater than x^2 so x cannot be greater than 1. Hence x must be less than -1. When x is less than -1, then x IS greater than x^3. Sufficient alone.

Answer (B)

Again, spend some time checking out the relations of x, x^2 and x^3 on the number line.
_________________

Bunuel Is x> x^3? Is x>x^3? --> is x^3-x<0? --> is (x+1)x(x-1)<0? is x<-1 or 0<x<1

when (x+1)x(x-1)<0,, doesnt it gives us the rage as x>-1 or x<1 ... because ..as you explained in an another question that

Intersection points are the roots of the equation x^2-4x+3=0, which are x_1=1 and x_2=3. "<" sign means in which range of x the graph is below x-axis. Answer is 1<x<3 (between the roots). From this i understood that "<" sign means roots to the RIGHT of the smaller root and to the LEFT of the bigger root).

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.
_________________

for x to be greater than x^3 Case 1: Either x < -1 or Case 2: 0 < x < 1

Statement 1: x < 0 x may be -0.5 or x may be -2 hence NOT SUFFICIENT

Statement 2: x^2 - x^3 > 2 For this statement to be true x < -1, (Just try some values to substitute in expression to check acceptable values of x), Hence SUFFICIENT

Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

Is x > x ^3 ?

(1) x < 0 (2) x^2 - x^3 > 2

When it comes to inequality questions, it is crucial that if range of que includes range of con, that con is sufficient. When you modify the original condition and the question, they become x^3-x<0?, x(x-1)(x+1)<0? -> x<-1, 0<x<1?. Then, there is 1 variable(x), which should match with the number of equations. So you need 1 more equation. For 1) 1 equation, for 2) 1 equation, which is likey to make D the answer. For 1), if x<0, the range of que doesn’t include the range of con, which is not sufficient. For 2), in x^3-x+2<0, (x+1)(x^2-2x+2)<0, x^2-2x+2=(x-1)^2+1 is derived, which is always bigger than 0. Then, x+1<0 -> x<-1, in which the range of que includes the range of con. Thus, it is sufficient and the answer is B.

-> For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.
_________________

For x^2-x^3>2 how did you directly arrive at the intervals <-1 between -1 and 1 and >1. When we deal with (1-x) >2 we get x <-1. But how did you chose the other point 1?[/quote]

i could not understand with those links... as x^2-x^3>2 we can write as X^2(1-X)>2 so roots are 0,1 So range will be x>1 or x<0 or in number line if i plot i get +ve values within 0<x<1(i m plotting with roots 0 and 1 only in consideration) Plz help......... secondly plz clear me also that the for selecting different roots is same for different inequality like x^2-x^3>2 and x^2-x^3>0

After days of waiting, sharing the tension with other applicants in forums, coming up with different theories about invites patterns, and, overall, refreshing my inbox every five minutes to...

I was totally freaking out. Apparently, most of the HBS invites were already sent and I didn’t get one. However, there are still some to come out on...

In early 2012, when I was working as a biomedical researcher at the National Institutes of Health , I decided that I wanted to get an MBA and make the...