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

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 < 0? [#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

combining xy is > 0

gmatclubot

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