What is the value of y-x^2-x? : GMAT Data Sufficiency (DS)
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# What is the value of y-x^2-x?

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What is the value of y-x^2-x? [#permalink]

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06 Jan 2013, 07:09
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Difficulty:

45% (medium)

Question Stats:

61% (02:18) correct 39% (01:16) wrong based on 222 sessions

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What is the value of y-x^2-x?

(1) y = -3x
(2) y = -4(x + 1)
[Reveal] Spoiler: OA

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Re: What is the value of y-x^2-x? [#permalink]

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06 Jan 2013, 07:55
4
KUDOS
We need to find whether info is sufficient to find value of y-x2-x.

We cant simplify the question stem further, so lets start with st1:
(1) y = -3x --> two vars 1 eq--> cant solve
(2) y = -4(x + 1) --> two vars 1 eq--> cant solve

1+2 together is solvable.
y=-3x and also y=-4x-4

so -3x=-4x-4
x=-4, y=12
we dont actually need to solve but for illustration i did. Knowing that we can solve them to get unique values of x and y is enough.

So 1 and 2 taken together are sufficient

Best Regards,
Mansoor

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Re: What is the value of y-x^2-x? [#permalink]

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18 Jul 2013, 13:17
Can someone please give a more in depth explanation to this. I would also appreciate if the question was $$using markup$$ because the expression in the question above is rather ambiguous.
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Re: What is the value of y-x^2-x? [#permalink]

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18 Jul 2013, 13:24
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Expert's post
aeglorre wrote:
Can someone please give a more in depth explanation to this. I would also appreciate if the question was $$using markup$$ because the expression in the question above is rather ambiguous.

What is the value of $$y-x^2-x$$?

(1) y = -3x --> the question becomes: what is the value of $$-3x-x^2-x$$. We need the value of x to answer this question. Not sufficient.

(2) y = -4(x + 1) --> the question becomes: what is the value of $$-4(x + 1)-x^2-x$$. We need the value of x to answer this question. Not sufficient.

(1)+(2) We have two distinct linear equations: $$y = -3x$$ and $$y = -4(x + 1)$$, thus we can solve for both variables and get the value of $$y-x^2-x$$. Sufficient.

Hope it's clear.
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Re: What is the value of y-x^2-x? [#permalink]

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18 Jul 2013, 21:12
Awesome, thanks a lot Bunuel. You are, as they say, "The Man".

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Re: What is the value of y-x^2-x? [#permalink]

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24 Oct 2013, 12:24
The explanation about linear equation is not clear
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Re: What is the value of y-x^2-x? [#permalink]

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25 Oct 2013, 01:04
Raihanuddin wrote:
The explanation about linear equation is not clear

If you have n distinct linear equations and n variables then you can solve for them. "Distinct linear equations" means that no equation can be derived with the help of others or by arithmetic operation (by multiplication, addition, ...).

We have two distinct linear equations: $$y = -3x$$ and $$y = -4(x + 1)$$. Solving gives: x=-4 and y=12.

Hope it's clear.
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Re: What is the value of y-x^2-x? [#permalink]

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21 May 2015, 02:41
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Re: What is the value of y-x^2-x? [#permalink]

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21 May 2015, 10:49
Hi All,

This DS question can be solved with a combination of TESTing VALUES and Algebra skills.

We're asked for the value of Y - X^2 - X.

Fact 1: Y = -3X

IF....
X = 0
Y = 0
The answer to the question is 0 - 0^2 - 0 = 0

IF...
X = 1
Y = -3
The answer to the question is -3 - 1^2 - 1 = -5
Fact 1 is INSUFFICIENT

Fact 2: Y = -4(X+1)

IF...
X = 0
Y = -4
The answer to the question is -4 - 0^2 - 0 = -4

IF...
X = 1
Y = -8
The answer to the question is -8 - 1^2 - 1 = -10
Fact 2 is INSUFFICIENT

Combined, we know...
Y = -3X
Y = -4(X+1)

Looking at this, you should recognize a "system" of equations - we can set the equations equal to one another...

-3X = -4X - 4
X = -4

With one fixed value for X, we can solve for Y:

Y = -3(-4) = 12

Thus, X = -4 and Y = 12, so we CAN answer the question.
Combined, SUFFICIENT

[Reveal] Spoiler:
C

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# Special Offer: Save $75 + GMAT Club Tests 60-point improvement guarantee www.empowergmat.com/ ***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*********************** Current Student Joined: 26 Apr 2015 Posts: 134 Followers: 0 Kudos [?]: 9 [0], given: 134 Re: What is the value of y-x^2-x? [#permalink] ### Show Tags 23 May 2015, 23:03 Bunuel wrote: aeglorre wrote: Can someone please give a more in depth explanation to this. I would also appreciate if the question was $$using markup$$ because the expression in the question above is rather ambiguous. What is the value of $$y-x^2-x$$? (1) y = -3x --> the question becomes: what is the value of $$-3x-x^2-x$$. We need the value of x to answer this question. Not sufficient. (2) y = -4(x + 1) --> the question becomes: what is the value of $$-4(x + 1)-x^2-x$$. We need the value of x to answer this question. Not sufficient. (1)+(2) We have two distinct linear equations: $$y = -3x$$ and $$y = -4(x + 1)$$, thus we can solve for both variables and get the value of $$y-x^2-x$$. Sufficient. Answer: C. Hope it's clear. Does this question belongs to the 700 level category? Seems pretty straightforward for a 700 leveler... Math Expert Joined: 02 Sep 2009 Posts: 36551 Followers: 7078 Kudos [?]: 93154 [0], given: 10553 Re: What is the value of y-x^2-x? [#permalink] ### Show Tags 24 May 2015, 05:56 dhruvmadra wrote: Bunuel wrote: aeglorre wrote: Can someone please give a more in depth explanation to this. I would also appreciate if the question was $$using markup$$ because the expression in the question above is rather ambiguous. What is the value of $$y-x^2-x$$? (1) y = -3x --> the question becomes: what is the value of $$-3x-x^2-x$$. We need the value of x to answer this question. Not sufficient. (2) y = -4(x + 1) --> the question becomes: what is the value of $$-4(x + 1)-x^2-x$$. We need the value of x to answer this question. Not sufficient. (1)+(2) We have two distinct linear equations: $$y = -3x$$ and $$y = -4(x + 1)$$, thus we can solve for both variables and get the value of $$y-x^2-x$$. Sufficient. Answer: C. Hope it's clear. Does this question belongs to the 700 level category? Seems pretty straightforward for a 700 leveler... The difficulty level is based on user attempts on this question. Check the stats in the original post. _________________ EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 8287 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: 340 Q170 V170 Followers: 380 Kudos [?]: 2459 [0], given: 163 Re: What is the value of y-x^2-x? [#permalink] ### Show Tags 24 May 2015, 09:47 Hi dhruvmadra, As you study, you're going to find that what you think is "hard" is not necessarily what the Test Makers 'define' as "hard" (and vice-versa). It's not practical to spend time trying to assess the difficulty level of any individual question. Since your goal is almost certainly to increase your scores, you should look at the types of questions that you're getting wrong and WHY you're getting them wrong. If you get a question wrong that you SHOULD have gotten correct (but you made a silly/little mistake), then I don't care what 'level' of question it is - you've got to work to keep those mistakes from happening (since too many little mistakes will kill your scores). GMAT assassins aren't born, they're made, Rich _________________ # Rich Cohen Co-Founder & GMAT Assassin # Special Offer: Save$75 + GMAT Club Tests

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Re: What is the value of y-x^2-x?   [#permalink] 24 May 2015, 09:47
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