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For x and y, what is the value of x?

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For x and y, what is the value of x?  [#permalink]

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New post Updated on: 10 Jul 2017, 12:09
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A
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C
D
E

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Question Stats:

38% (01:29) correct 63% (01:14) wrong based on 84 sessions

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For x and y, what is the value of x?

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

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Originally posted by MathRevolution on 05 Jul 2017, 01:03.
Last edited by MathRevolution on 10 Jul 2017, 12:09, edited 1 time in total.
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Re: For x and y, what is the value of x?  [#permalink]

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New post 05 Jul 2017, 01:26
1) (x-3)(x+y)=0
Since we don't know the value of y, we cannot say what is the value of x
as x=3 or x=-y(without knowing the value of y, we can't clearly find out the value of x(Insufficient)

2) (x-3)(2x+y)=0
Since we don't know the value of y, we cannot say what is the value of x
as x=3 or x=-y/2(without knowing the value of y, we can't clearly find out the value of x(Insufficient)

On combining the information in both the statements,
we know x=3 and x=-y and -y/2
This is possible only when y = 0, we can clearly tell what the value of x is(Sufficient) (Option C)
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Re: For x and y, what is the value of x?  [#permalink]

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New post 06 Jul 2017, 10:46
1
MathRevolution But what if y=0?? In that case ,ans. will be E. I think you should have mentioned that y is not 0 in the ques stem.
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For x and y, what is the value of x?  [#permalink]

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New post Updated on: 10 Jul 2017, 12:13
==> In the original condition, there are 2 variables (x,y) and in order to match the number of variables to the number of equations, there must be 2 equations. Since there is 1 for con 1) and 1 for con 2), C is most likely to be the answer. By solving con 1) and con 2), you have \(x=3\) or \(x = y = 0\). Thus both conditions 1) & 2) together are not sufficient.

Therefore, the answer is E.
Answer: E
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Originally posted by MathRevolution on 07 Jul 2017, 01:05.
Last edited by MathRevolution on 10 Jul 2017, 12:13, edited 1 time in total.
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Re: For x and y, what is the value of x?  [#permalink]

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New post 08 Jul 2017, 07:41
On solving we get
x = 3
OR
x = -y, -y/2 --> Solving this gives us y = 0 --> This in turn means x(x-3) = 0
Combining now gives two values for x --> 0 and 3.

The question stem does not mention that x cannot be 0. How then are we arriving at C as the answer when there are clearly 2 values.

Bunuel could you please weigh in here as well, incase i am missing something.
Making mistakes in questions by what seem like legitimate sources, means we end up learning something wrong, as is the case here. If i am wrong then i would like to understand how.

MathRevolution
Quote:
In the original condition, there are 2 variables (x,y) and in order to match the number of variables to the number of equations, there must be 2 equations. Since there is 1 for con 1) and 1 for con 2), C is most likely to be the answer. By solving con 1) and con 2), you get x=3, which is unique and sufficient.

Therefore, the answer is C.
Answer: C


Would you mine explaining this, wrt what i have mentioned?
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Re: For x and y, what is the value of x?  [#permalink]

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New post 09 Jul 2017, 04:57
What if y = 0 ?, then X can be 0 or 3 as well. Please explain!
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Re: For x and y, what is the value of x?  [#permalink]

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New post 09 Jul 2017, 18:55
I am not able to understand how x is only equal to 3? Both the statements are insufficient on their own and when you combine them, you get x=3 and x=-y and -y/2. Shouldn't the answer be E? X has two values here. Please help me!
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Re: For x and y, what is the value of x?   [#permalink] 09 Jul 2017, 18:55
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