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# M22-03

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Math Expert
Joined: 02 Sep 2009
Posts: 44656

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16 Sep 2014, 01:15
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Difficulty:

25% (medium)

Question Stats:

67% (00:48) correct 33% (01:13) wrong based on 103 sessions

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What is the value of $$x$$ ?

(1) $$x^4 = |x|$$

(2) $$x^2 \gt x$$
[Reveal] Spoiler: OA

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Math Expert
Joined: 02 Sep 2009
Posts: 44656

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16 Sep 2014, 01:15
Expert's post
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Official Solution:

(1) $$x^4 = |x|$$. This statement implies that $$x=-1$$, $$x=0$$, or $$x=1$$. Not sufficient.

(2) $$x^2 \gt x$$. Rearrange and factor out $$x$$ to get $$x(x-1) \gt 0$$. The roots are $$x=0$$ and $$x=1$$, "$$\gt$$" sign means that the given inequality holds true for: $$x \lt 0$$ and $$x \gt 1$$. Not sufficient.

(1)+(2) The only value of $$x$$ from (1) which is in the range from (2) is $$x=-1$$. Sufficient.

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Joined: 16 Feb 2014
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09 Nov 2014, 21:42
Thanks for Explanation! I did not understand following part

" The roots are x=0 and x=1, $$"\gt"$$ sign means that the given inequality holds true for: $$x \lt 0$$ and $$x \gt 1$$."

I thought $$x(x-1) \gt 0$$ would mean $$x \gt 0$$ and $$x \gt 1$$

Please suggest. Also how did we get -1 as final answer. As per statement (2) $$x \gt 1$$.

Thanks

Bunuel wrote:
Official Solution:

(1) $$x^4 = |x|$$. This statement implies that $$x=-1$$, $$x=0$$, or $$x=1$$. Not sufficient.

(2) $$x^2 \gt x$$. Rearrange and factor out $$x$$ to get $$x(x-1) \gt 0$$. The roots are $$x=0$$ and $$x=1$$, "$$\gt$$" sign means that the given inequality holds true for: $$x \lt 0$$ and $$x \gt 1$$. Not sufficient.

(1)+(2) The only value of $$x$$ from (1) which is in the range from (2) is $$x=-1$$. Sufficient.

Math Expert
Joined: 02 Sep 2009
Posts: 44656

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10 Nov 2014, 02:57
Sky78 wrote:
Thanks for Explanation! I did not understand following part

" The roots are x=0 and x=1, $$"\gt"$$ sign means that the given inequality holds true for: $$x \lt 0$$ and $$x \gt 1$$."

I thought $$x(x-1) \gt 0$$ would mean $$x \gt 0$$ and $$x \gt 1$$

Please suggest. Also how did we get -1 as final answer. As per statement (2) $$x \gt 1$$.

Thanks

Bunuel wrote:
Official Solution:

(1) $$x^4 = |x|$$. This statement implies that $$x=-1$$, $$x=0$$, or $$x=1$$. Not sufficient.

(2) $$x^2 \gt x$$. Rearrange and factor out $$x$$ to get $$x(x-1) \gt 0$$. The roots are $$x=0$$ and $$x=1$$, "$$\gt$$" sign means that the given inequality holds true for: $$x \lt 0$$ and $$x \gt 1$$. Not sufficient.

(1)+(2) The only value of $$x$$ from (1) which is in the range from (2) is $$x=-1$$. Sufficient.

Inequality tips: tips-and-hints-for-specific-quant-topics-with-examples-172096.html#p1379270
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Joined: 01 Oct 2014
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21 Jun 2016, 07:13
I think this is a high-quality question and the explanation isn't clear enough, please elaborate. Not able to understand the explanation
Math Expert
Joined: 02 Sep 2009
Posts: 44656

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21 Jun 2016, 07:18
I think this is a high-quality question and the explanation isn't clear enough, please elaborate. Not able to understand the explanation

Please check alternate solutions here: what-is-the-value-of-x-147037.html
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Senior Manager
Joined: 08 Jun 2015
Posts: 482
Location: India
GMAT 1: 640 Q48 V29

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27 Dec 2017, 08:31
+1 for C. From the first statement x=-1,0, or 1. From second statement , x<0 or x>1. Each statement alone is not sufficient. Combine the two, x=-1. Hence option C.
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" The few , the fearless "

Intern
Joined: 13 Oct 2017
Posts: 40

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16 Feb 2018, 06:51
Bunuel wrote:
Sky78 wrote:
Thanks for Explanation! I did not understand following part

" The roots are x=0 and x=1, $$"\gt"$$ sign means that the given inequality holds true for: $$x \lt 0$$ and $$x \gt 1$$."

I thought $$x(x-1) \gt 0$$ would mean $$x \gt 0$$ and $$x \gt 1$$

Please suggest. Also how did we get -1 as final answer. As per statement (2) $$x \gt 1$$.

Thanks

Bunuel wrote:
Official Solution:

(1) $$x^4 = |x|$$. This statement implies that $$x=-1$$, $$x=0$$, or $$x=1$$. Not sufficient.

(2) $$x^2 \gt x$$. Rearrange and factor out $$x$$ to get $$x(x-1) \gt 0$$. The roots are $$x=0$$ and $$x=1$$, "$$\gt$$" sign means that the given inequality holds true for: $$x \lt 0$$ and $$x \gt 1$$. Not sufficient.

(1)+(2) The only value of $$x$$ from (1) which is in the range from (2) is $$x=-1$$. Sufficient.

Inequality tips: http://gmatclub.com/forum/tips-and-hint ... l#p1379270

Hi Bunuel,

I too have exactly the same question as the previous person...I went through the links provided and still cannot understand why in statement 2, x is not either greater than 0 or greater than 1. I then got confused as to how you got to the answer being x= (-1).

Would really appreciate a breakdown of the above queries please.

Thanks,

Tosin
Math Expert
Joined: 02 Sep 2009
Posts: 44656

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16 Feb 2018, 06:57
Expert's post
1
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ttaiwo wrote:
Hi Bunuel,

I too have exactly the same question as the previous person...I went through the links provided and still cannot understand why in statement 2, x is not either greater than 0 or greater than 1. I then got confused as to how you got to the answer being x= (-1).

Would really appreciate a breakdown of the above queries please.

Thanks,

Tosin

This is explained in detail in the links provided.

x > 0 or x > 1 doe not make any sense. Is x > 0? So, could it be 0.5? Or is x > 1?

$$x(x-1) \gt 0$$ --> x and x - 1 have the same sign.

x > 0 and x - 1 > 0 --> x > 0 and x > 1. Simultaneously to be true x > 1 has to be true.
x < 0 and x - 1 < 0 --> x < 0 and x < 1. Simultaneously to be true x < 0 has to be true.

So, $$x(x-1) \gt 0$$ is true for x < 0 and x > 1.
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Intern
Joined: 13 Oct 2017
Posts: 40

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17 Feb 2018, 03:58
Bunuel wrote:
ttaiwo wrote:
Hi Bunuel,

I too have exactly the same question as the previous person...I went through the links provided and still cannot understand why in statement 2, x is not either greater than 0 or greater than 1. I then got confused as to how you got to the answer being x= (-1).

Would really appreciate a breakdown of the above queries please.

Thanks,

Tosin

This is explained in detail in the links provided.

x > 0 or x > 1 doe not make any sense. Is x > 0? So, could it be 0.5? Or is x > 1?

$$x(x-1) \gt 0$$ --> x and x - 1 have the same sign.

x > 0 and x - 1 > 0 --> x > 0 and x > 1. Simultaneously to be true x > 1 has to be true.
x < 0 and x - 1 < 0 --> x < 0 and x < 1. Simultaneously to be true x < 0 has to be true.

So, $$x(x-1) \gt 0$$ is true for x < 0 and x > 1.

Thanks a lot...now understood.
Re: M22-03   [#permalink] 17 Feb 2018, 03:58
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# M22-03

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