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# What is y?

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Intern
Status: Aiming for 750+
Joined: 16 Oct 2013
Posts: 21
GMAT Date: 05-05-2014

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13 Dec 2013, 16:31
00:00

Difficulty:

35% (medium)

Question Stats:

64% (01:11) correct 36% (00:50) wrong based on 129 sessions

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What is y?

(1) x - y = 1
(2) xy = 12

I understand the question but my doubt however is:
The MGMAT Guide says,
Quote:
Even when the equations are combined, they do not provide enough information to find y, and the
. I do not understand why it says that because when I combine both the equations, I get a quadratic equation. I solve it and I get two answers y = -4 or y = 3. So, my take is using both the equations I am able to find the value of y. So, why is the correct answer E and why not C? Thank you!
Intern
Joined: 05 Oct 2013
Posts: 21
Re: What is y? (1) x - y = 1 (2)x y = 12  [#permalink]

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14 Dec 2013, 04:36
1
flower07 wrote:
What is y?

(1) x - y = 1
(2)x y = 12

I understand the question but my doubt however is:
The MGMAT Guide says,
Quote:
Even when the equations are combined, they do not provide enough information to find y, and the
. I do not understand why it says that because when I combine both the equations, I get a quadratic equation. I solve it and I get two answers y = -4 or y = 3. So, my take is using both the equations I am able to find the value of y. So, why is the correct answer E and why not C? Thank you!

You got two possible values of y, which means that you don't know which one must be y (only one value counted!). The answer should be E
Math Expert
Joined: 02 Sep 2009
Posts: 54544

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14 Dec 2013, 06:12
3
flower07 wrote:
What is y?

(1) x - y = 1
(2) xy = 12

I understand the question but my doubt however is:

The MGMAT Guide says,
Quote:
Even when the equations are combined, they do not provide enough information to find y, and the
. I do not understand why it says that because when I combine both the equations, I get a quadratic equation. I solve it and I get two answers y = -4 or y = 3. So, my take is using both the equations I am able to find the value of y. So, why is the correct answer E and why not C? Thank you!

When a DS question asks about the value of some variable, then the statement is sufficient ONLY if you can get the single numerical value of this variable.

Since you get TWO possible values of y, the statements are not sufficient.

Hope it's clear.
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Manager
Status: Work hard in silence, let success make the noise
Joined: 25 Nov 2013
Posts: 131
Location: India
Concentration: Finance, General Management
GMAT 1: 540 Q50 V15
GMAT 2: 640 Q50 V27
GPA: 3.11
WE: Consulting (Computer Software)

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14 Dec 2013, 11:01
1
I marked E since we are getting 2 values of y(3,-4) even after combining both the equations.
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Sahil Chaudhary
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Joined: 12 Nov 2016
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GMAT 1: 650 Q43 V37
GRE 1: Q157 V158
GPA: 2.66

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24 May 2017, 12:33
flower07 wrote:
What is y?

(1) x - y = 1
(2) xy = 12

I understand the question but my doubt however is:
The MGMAT Guide says,
Quote:
Even when the equations are combined, they do not provide enough information to find y, and the
. I do not understand why it says that because when I combine both the equations, I get a quadratic equation. I solve it and I get two answers y = -4 or y = 3. So, my take is using both the equations I am able to find the value of y. So, why is the correct answer E and why not C? Thank you!

You just have to pay attention to the mild trap this question is baiting you into - it wants to make sure you are remembering the commutative instead of making assumptions. For example,

(4)3= 12
4-3 = 1

BUT

-3(-4)=12
-3 --4= 1
Director
Joined: 12 Nov 2016
Posts: 725
Location: United States
Schools: Yale '18
GMAT 1: 650 Q43 V37
GRE 1: Q157 V158
GPA: 2.66

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08 Sep 2017, 20:35
flower07 wrote:
What is y?

(1) x - y = 1
(2) xy = 12

I understand the question but my doubt however is:
The MGMAT Guide says,
Quote:
Even when the equations are combined, they do not provide enough information to find y, and the
. I do not understand why it says that because when I combine both the equations, I get a quadratic equation. I solve it and I get two answers y = -4 or y = 3. So, my take is using both the equations I am able to find the value of y. So, why is the correct answer E and why not C? Thank you!

Nice trick here...classic "C" trap

St 1

x-y =1 - clearly too many possibilities

insuff

St 2

xy = 12

clearly too many possibilities

insuff

St 1 and St 2

This question wants you to assume that the answer should be 4 and 3...however the answer can also be -3 and -4

E
Re: What is y?   [#permalink] 08 Sep 2017, 20:35
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