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# If x=y^2

Author Message
Study Buddy Forum Moderator
Joined: 04 Sep 2016
Posts: 1299
Location: India
WE: Engineering (Other)

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02 Mar 2018, 17:04
00:00

Difficulty:

45% (medium)

Question Stats:

71% (00:57) correct 29% (00:59) wrong based on 17 sessions

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If x = $$y^2$$, what is the value of y – x?

(1) x = 4

(2) x + y = 2

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Study Buddy Forum Moderator
Joined: 04 Sep 2016
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02 Mar 2018, 20:31
pushpitkc niks18 Hatakekakashi
amanvermagmat Bunuel chetan2u

Any another approach than number picking here?

I tried below, but could not get to OE:

St 1. From x = 4, we get y = +/- 2
Question asks: y-x or y - $$y^2$$ or y * (y-1) = ?
since we have two values of y from st 1 , this st will not lead
to UNIQUE ans and hence is insuff.

St 2: x+y =2
$$y^2$$ + y = 2
y * (y+1) =2
How to proceed from here?
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DS Forum Moderator
Joined: 21 Aug 2013
Posts: 1434
Location: India

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02 Mar 2018, 21:19
y^2 + y = 2
y^2 + y - 2 = 0
Solve this quadratic equation and again you will get two values of y as:

y=1 and y=-2

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Study Buddy Forum Moderator
Joined: 04 Sep 2016
Posts: 1299
Location: India
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02 Mar 2018, 21:29
Thanks amanvermagmat

Is my analysis of St 1 correct or you have better approach?
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Senior PS Moderator
Joined: 26 Feb 2016
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02 Mar 2018, 21:38

St2 : This can be rewritten as y = 2 - x
Therefore, the value y - x will take is 2 - x - x = 2 - 2x.
Since we don't know the value of x, we cannot come to a conclusive answer.

But then on combining the information from both the statements,
we have a unique solution for y - x = 2 - 2(4) = -6

That's why the answer should be Option C. Hope this helps!
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Math Expert
Joined: 02 Sep 2009
Posts: 52363

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03 Mar 2018, 01:06
If x = $$y^2$$, what is the value of y – x?

(1) x = 4

(2) x + y = 2

This question is discussed here: if-x-y-2-what-is-the-value-of-y-x-1-x-4-2-x-y-206393.html Hope it helps.

Please search before posting and name topics properly. The name of this topic should have been: "If x = y^2, what is the value of y – x? (1) x = 4 (2) x + y = 2" NOT "If x=y^2". Such short names mess up similar topics search block. Thank you.

TOPIC IS LOCKED AND ARCHIVED.

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

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Re: If x=y^2 &nbs [#permalink] 03 Mar 2018, 01:06
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