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Is x positive?

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Is x positive?  [#permalink]

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New post 07 Jan 2017, 04:07
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A
B
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D
E

Difficulty:

  65% (hard)

Question Stats:

39% (00:41) correct 61% (00:43) wrong based on 101 sessions

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Is x positive?

(1) \(x*|x|=x^2\)

(2) \(x^2*|x|=x^3\)

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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


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Re: Is x positive?  [#permalink]

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New post 07 Jan 2017, 05:22
chetan2u wrote:
Is x positive?

(1) \(x*|x|=x^2\)

(2) \(x^2*|x|=x^3\)

Self made



(1) \(x\times |x| = x^2 \implies x(x-|x|)=0\)

Hence \(x=0\) or \(x=|x| \implies x \geq 0\).
In all cases, we have \(x \geq 0\), insufficient.

(2) \(x^2 \times |x| = x^3 = x^2 \times x \implies x^2 (|x|-x)=0\)

Hence \(x^2=0\implies x=0\)
or \(x=|x| \implies x\geq 0\)
In all cases, we have \(x \geq 0\). Insufficient.

Combine (1) and (2), we still have \(x \geq 0\). Insufficient.

The answer is E.
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Re: Is x positive?  [#permalink]

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New post 18 Dec 2017, 07:51
chetan2u wrote:
Is x positive?

(1) \(x*|x|=x^2\)

(2) \(x^2*|x|=x^3\)

Self made



Very important to NOT miss out all possible values of x- integer, fraction, positive , negative ,0 etc
70% gone wrong means we tend to OVERLOOK 0 as a value..

(1) \(x*|x|=x^2\)
x is surely non-negative BUT it can be 0 or positive
Insuff

(2) \(x^2*|x|=x^3\)
again x can be positive or 0
insuff

combined x can still be o, ans will be NO
x can be positive, ans will be YES
insuff

E
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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


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Re: Is x positive?  [#permalink]

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New post 18 Dec 2017, 08:03
What is the need of considering fraction/integer ?

Statement 1 : it shows that x is non negative, it can be 0 or any positive number.
Statement 2: it shows that x is non negative, it can be 0 or any positive number.
Statement 1 & 2 : it shows that x is non negative, it can be 0 or any positive number.
hence it is not sufficient that x is positive

chetan2u wrote:
chetan2u wrote:
Is x positive?

(1) \(x*|x|=x^2\)

(2) \(x^2*|x|=x^3\)

Self made



Very important to NOT miss out all possible values of x- integer, fraction, positive , negative ,0 etc
70% gone wrong means we tend to OVERLOOK 0 as a value..

(1) \(x*|x|=x^2\)
x is surely non-negative BUT it can be 0 or positive
Insuff

(2) \(x^2*|x|=x^3\)
again x can be positive or 0
insuff

combined x can still be o, ans will be NO
x can be positive, ans will be YES
insuff

E

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DS Forum Moderator
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Joined: 27 Oct 2017
Posts: 674
Location: India
Concentration: International Business, General Management
GPA: 3.64
WE: Business Development (Energy and Utilities)
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Re: Is x positive?  [#permalink]

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New post 18 Dec 2017, 08:45
you are right, sometimes we make mistakes just because we take x as integers.
Thank you.

chetan2u wrote:
gmatbusters wrote:
What is the need of considering fraction/integer ?


chetan2u wrote:


Very important to NOT miss out all possible values of x- integer, fraction, positive , negative ,0 etc
70% gone wrong means we tend to OVERLOOK 0 as a value..

(1) \(x*|x|=x^2\)
x is surely non-negative BUT it can be 0 or positive
Insuff

(2) \(x^2*|x|=x^3\)
again x can be positive or 0
insuff

combined x can still be o, ans will be NO
x can be positive, ans will be YES
insuff

E


Hi...
The point is general.
Specific to this Q is in colored portion which talks of only 0

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Re: Is x positive? &nbs [#permalink] 18 Dec 2017, 08:45
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