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.

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:

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
09 Aug 2009, 04:18

lbsgmat wrote:

If x and y are integers and xy does not equal 0, is xy < 0?

(1) y = x^4 – x^3 (2) x is to the right of 0 on the number line.

my answer is C

St 1. x can be any number but -1 or 0 (according to the question stem). Any other interger +ve or -ve will produce a +ve y however it is not sufficient since if x is +ve then xy>0, if x is -ve then xy<0 INSF

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
09 Aug 2009, 05:49

yezz wrote:

lbsgmat wrote:

If x and y are integers and xy does not equal 0, is xy < 0?

(1) y = x^4 – x^3 (2) x is to the right of 0 on the number line.

does xy have different signs

y = x^3(x-1), if x -ve then y is +ve , and if x is +ve we have 2 cases y can be either -ve or +ve (-ve if /x/<1)

from 2

x is +ve....insuff

both together

still insuff... E

Marked in Red, since x and y are integers we have to ignore the condition |x|<1. So C(edited) should be the answer as y will always be +ve for any integer x other than 0.

Last edited by Economist on 09 Aug 2009, 11:53, edited 1 time in total.

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
09 Aug 2009, 06:04

Economist wrote:

yezz wrote:

lbsgmat wrote:

If x and y are integers and xy does not equal 0, is xy < 0?

(1) y = x^4 – x^3 (2) x is to the right of 0 on the number line.

does xy have different signs

y = x^3(x-1), if x -ve then y is +ve , and if x is +ve we have 2 cases y can be either -ve or +ve (-ve if /x/<1)

from 2

x is +ve....insuff

both together

still insuff... E

Marked in Red, since x and y are integers we have to ignore the condition |x|<1. So A should be the answer as y will always be +ve for any integer x other than 0.

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
20 Aug 2009, 10:35

If x and y are integers and xy does not equal 0, is xy < 0?

(1) y = x^4 – x^3 (2) x is to the right of 0 on the number line.

We know xy not equals 0 , it can be +ve or -ve. Possible scenarios are X(+,+,-,-) , Y (+,-,-,+)

Now from Stmt 1 y = X^3(X-1) if X is +ve, then the question is X>1. If yes then Y will be +ve , if not then 0<x<1 then Y will be - ve . No information regarding value of x is given .

If X is -ve, then Y will be + ve irrespective of value of X . So there are two cases with this statement so statement is no sufficient.

From statement X is to right of 0 , and from question statement xy not equals 0 that means neither x nor y is zero.

Combining these two statement means X is positive and is greater than 1 , so xy will be positive

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
21 Aug 2009, 16:50

1

This post received KUDOS

C fo shiz.

I almost got tripped up in my own trickyness here - need to note that X and Y are integers, therefore 0 < x <1 is not possible. Once you have eliminated this condition, the two statements are sufficient.

These are key things to look out for:

If X and Y are integers If X and Y are positive integers If X and Y and different integers

My big tip here is to pay attention to the question and go back and double check the parameters for X and Y.

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
24 Aug 2009, 17:37

I got C too..Correct answer? 1.can solve to y = x^4 - x^3 = x^3(x-1)..so xy = x^4(x-1)..whether xy is +ve or -ve depends on value of x,as x^ 4 will always be +ve 2.x is +ve,dont know anything about y

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
20 Nov 2011, 14:10

I) x^4-x^3 is always greater than or equal to 0. But in both cases xy must be equal to 0. So this case is impossible. That means y is always greater than 0. INSUFF. 2) if x is at right of 0 that means x is greater than 0.INSUFF. Both together, x>0 and y>0 xy>0. C

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
30 Nov 2011, 09:35

1

This post received KUDOS

1) says y=X^4-x^3 or y=x^3(x-1) multiply both sides by x xy=x^4(x-1) since we do not know anything about x it can be positive or negative. x^4 is always +ve. hence insufficient 2) Says X is >=1 does not say anything about y. Hence insufficient

Both together, xy=x^4(x-1) x^4 is def. +ve (x-1) >=0 if x>=1

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
27 Aug 2014, 06:20

Quote:

I think the OA is incorrect here.

1) y = x^4 - x^3. Thus, we know that xy = x(x^4 - x^3) = x^5 - x^4 = x^4(x - 1). Our question is then, is x^4(x-1)<0?

Since we have no idea about x this is clearly insufficient.

2) If y is positive, then NO, but if y is negative then YES. Insufficient.

Taking the two statements together. We need to find out if x^4(x - 1)<0.

To find where this function changes signs, we set it equal to zero and then test values between our critical points. x^4(x-1)=0 gives us x = 0 and x = 1.

Testing on our number line: for x<0 we see that xy = x^4(x-1) is negative; for 0<x<1, we see that xy is STILL negative; for x>1 we see that xy IS POSITIVE.

Therefore, simply knowing that x is positive does not provide us with enough information. We still need to know whether x>1 or x<1.

Answer: E

Edit: Just saw that x and y are integers! Very sneaky! I'm leaving this post because I think it's valuable to see this thought process anyway.

Re: If x and y are integers and xy does not equal 0, is xy < [#permalink]
18 Sep 2014, 09:09

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. _________________