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Is xy < 0 ?

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Is xy < 0 ? [#permalink]

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New post 08 May 2012, 03:25
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A
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D
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Re: Is xy < 0 ? [#permalink]

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New post 08 May 2012, 09:34
Statement 1 => x = y = 0. Sufficient.
Statement 2 => x = y = 0. Sufficient.

Choice D.
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Last edited by GyanOne on 09 May 2012, 03:08, edited 1 time in total.
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Re: Is xy < 0 ? [#permalink]

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New post 08 May 2012, 12:44
GyanOne wrote:
Statement 1 => |y|/|x| = -5 => x and y are of opposite signs => xy<0. Sufficient.
Statement 2 => |x|/|y| = -5 => x and y are of opposite signs => xy<0. Sufficient.

Choice D.


D as well,
but think about it -
(1) 5|x| + |y| = 0
When is a sum equal to zero? one is negative, one is positive. But || (absolute value?, not sure what is the English for it) can't be negative, thus both |x| an |y| should be equal to zero. This means xy clearly is not < 0, but equal to zero. Sufficient
(2) same thing for this option
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Re: Is xy < 0 ? [#permalink]

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New post 09 May 2012, 02:42
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GyanOne wrote:
Statement 1 => |y|/|x| = -5 => x and y are of opposite signs => xy<0. Sufficient.
Statement 2 => |x|/|y| = -5 => x and y are of opposite signs => xy<0. Sufficient.

Choice D.


That's not correct.

Is xy < 0?

(1) 5|x| + |y| = 0. Since absolute value is always non-negative then we have that the sum of two non-negative values (5|x| and |y|) is zero, which is only possible if each is zero --> x=y=0 --> xy=0. Sufficient.

(2) |x| + 5|y| = 0. The same here. Sufficient.

Answer: D.
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Re: Is xy < 0 ? [#permalink]

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New post 27 Nov 2012, 19:32
This was a good problem.

carcass wrote:
Is xy < 0?

(1) 5|x| + |y| = 0

(2) |x| + 5|y| = 0
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Re: Is xy < 0 ? [#permalink]

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Re: Is xy < 0 ? [#permalink]

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New post 26 Sep 2014, 14:12
question is X and y are opposite sign?

stmt 1 : 5x=-y
x/y = - 5, x and y are opposite sign , sufficient.

stmt2L x=-5y, x/y = -5 , x and y are opposite sign , sufficient.


if x and y are same sign x/y will always be positive.
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Re: Is xy < 0 ? [#permalink]

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New post 13 Mar 2016, 22:24
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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 xy < 0?


In the original condition, there are 2 variables(x,y), which should match with the number of equations. So you need 2 equations. For 1) 1 equation, for 2) 1 equation, which is likely to make C the answer. When 1) & 2), 1)=2) -> x=y=0, which is no and sufficient.
Thus, D is the answer.


 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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Re: Is xy < 0 ?   [#permalink] 13 Mar 2016, 22:24
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