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What is y?

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Intern
Intern
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Status: Aiming for 750+
Joined: 16 Oct 2013
Posts: 21

Kudos [?]: 26 [0], given: 15

GMAT Date: 05-05-2014
What is y? [#permalink]

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New post 13 Dec 2013, 16:31
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

58% (00:54) correct 42% (00:34) wrong based on 115 sessions

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What is y?

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

I understand the question but my doubt however is:
[Reveal] Spoiler:
The MGMAT Guide says,
Quote:
Even when the equations are combined, they do not provide enough information to find y, and the
answer is (E).
. 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!
[Reveal] Spoiler: OA

Kudos [?]: 26 [0], given: 15

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Intern
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Joined: 05 Oct 2013
Posts: 21

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Re: What is y? (1) x - y = 1 (2)x y = 12 [#permalink]

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

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

I understand the question but my doubt however is:
[Reveal] Spoiler:
The MGMAT Guide says,
Quote:
Even when the equations are combined, they do not provide enough information to find y, and the
answer is (E).
. 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

Kudos [?]: 11 [1], given: 0

Expert Post
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Math Expert
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V
Joined: 02 Sep 2009
Posts: 42247

Kudos [?]: 132677 [3], given: 12331

Re: What is y? [#permalink]

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New post 14 Dec 2013, 06:12
3
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KUDOS
Expert's post
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
answer is (E).
. 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
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Status: Work hard in silence, let success make the noise
Joined: 25 Nov 2013
Posts: 157

Kudos [?]: 82 [1], given: 84

Location: India
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Re: What is y? [#permalink]

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New post 14 Dec 2013, 11:01
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I marked E since we are getting 2 values of y(3,-4) even after combining both the equations.
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Director
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S
Joined: 12 Nov 2016
Posts: 794

Kudos [?]: 36 [0], given: 165

Re: What is y? [#permalink]

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New post 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:
[Reveal] Spoiler:
The MGMAT Guide says,
Quote:
Even when the equations are combined, they do not provide enough information to find y, and the
answer is (E).
. 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

Kudos [?]: 36 [0], given: 165

Director
Director
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S
Joined: 12 Nov 2016
Posts: 794

Kudos [?]: 36 [0], given: 165

Re: What is y? [#permalink]

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New post 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:
[Reveal] Spoiler:
The MGMAT Guide says,
Quote:
Even when the equations are combined, they do not provide enough information to find y, and the
answer is (E).
. 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

Kudos [?]: 36 [0], given: 165

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