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Is y = 3?

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Is y = 3? [#permalink]

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New post 14 Feb 2016, 05:32
Expert's post
4
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A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

51% (00:25) correct 49% (00:23) wrong based on 124 sessions

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Re: Is y = 3? [#permalink]

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New post 14 Feb 2016, 11:46
(1) (y - 3)(x - 4) = 0
either y-3 = 0 or x-4 =0
=> either y=3 or x=4
Not sufficient

(2) (x - 4) = 0
=> x=4
Not sufficient as we have no information about value of y
Answer E
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Re: Is y = 3? [#permalink]

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New post 15 Feb 2016, 00:03
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

Is y = 3?

(1) (y - 3)(x - 4) = 0
(2) (x - 4) = 0


In the original condition, there is 1 variable(x). But, on the whole, there are 2 variables(x,y), which should match with the number of equations. So you need 1 equation. For 1) 1 equation, for 2) 1 equation, which is likely to make C the answer. When 1) & 2), if x=4, y=3 -> yes and y=4 -> no, which is not sufficient. Therefore, the answer is E.


 For cases where we need 2 more equations, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
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How to do this  [#permalink]

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New post 02 Apr 2017, 08:38
Guys! Try this DS problem .
*Is y = 3?*
1. (y - 3)(x - 4) = 0
2. (x - 4) = 0

Sent from my Redmi Note 3 using GMAT Club Forum mobile app
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Re: Is y = 3? [#permalink]

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New post 02 Apr 2017, 08:44
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Re: Is y = 3? [#permalink]

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New post 03 Apr 2017, 11:39
janakan91 wrote:
Guys! Try this DS problem .
*Is y = 3?*
1. (y - 3)(x - 4) = 0
2. (x - 4) = 0

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janakan91

combining both
if x=4 then y may be =3 or any other value

Ans E
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Re: Is y = 3? [#permalink]

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New post 12 Mar 2018, 14:24
Hi All,

This DS question is based on the concept of Quadratics, but you have to be very careful with the information that you're given.

The question asks if Y = 3. This is a YES/NO question.

Fact 1: (Y - 3)(X - 4) = 0

This means that EITHER Y = 3 OR X = 4.

If Y = 3, then the answer to the question is YES.
If X = 4, then Y could be ANYTHING and the answer to the question could be YES (If Y = 3) or NO (If Y = anything else).
Fact 1 is INSUFFICIENT

Fact 2: (X - 4) = 0

This tells us that X = 4, but tells us nothing about Y.
Fact 2 is INSUFFICIENT

Combined, we know that X = 4, but we still don't know anything about Y. We run into the same situation as in Fact 1. Y might = 3, but it might be something else.
Combined, INSUFFICIENT.

Final Answer:
[Reveal] Spoiler:
E


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Re: Is y = 3?   [#permalink] 12 Mar 2018, 14:24
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