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Intern  G
Joined: 20 Aug 2019
Posts: 41
GPA: 3.9
Is |x – y| > |x| – |y|? (1) y < x (2) x y < 0  [#permalink]

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Difficulty:   35% (medium)

Question Stats: 82% (01:46) correct 18% (02:23) wrong based on 11 sessions

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Is $$|x – y| > |x| – |y|$$?
(1) $$y < x$$
(2) $$x y < 0$$
SVP  D
Joined: 03 Jun 2019
Posts: 2001
Location: India
GMAT 1: 690 Q50 V34 WE: Engineering (Transportation)
Re: Is |x – y| > |x| – |y|? (1) y < x (2) x y < 0  [#permalink]

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1
naju wrote:
Is $$|x – y| > |x| – |y|$$?
(1) $$y < x$$
(2) $$x y < 0$$

Asked: Is $$|x – y| > |x| – |y|$$?

(1) $$y < x$$
If x=3;y=1; |x-y| =2; |x|-|y| = 2
But if x=3;y=-1; |x-y| =4; |x|-|y| = 2
Not sufficient

(2) $$x y < 0$$
x and y have opposite signs
If x=3; y=-2; |x-y| =5; |x|-|y| = 1
If x= -3; y=2; |x-y| = 5; |x|-|y|=1
|x-y| >|x|-|y|
Sufficient

IMO B

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GMAT Tutor B
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Is |x – y| > |x| – |y|? (1) y < x (2) x y < 0  [#permalink]

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naju wrote:
Is $$|x – y| > |x| – |y|$$?
(1) $$y < x$$
(2) $$x y < 0$$

Plugging in numbers is good way to approach this question. However, you may try and remember 2 properties that are quite useful:

#1. $$|x| + |y| ≥ |x + y|$$
Note: The '>' holds when x and y are of opposite signs i.e. one is positive and the other is negative
The '=' holds when x and y are of same signs i.e. both are positive or both are negative
Example: |5| + |2| = |5 + 2|; |-5| + |-2| = |-5 - 2|; |5| + |-2| > |5 - 2|

#2. $$|x| - |y| ≤ |x - y|$$ (assuming |x| is greater than |y|)
Note: The '<' holds when x and y are of opposite signs i.e. one is positive and the other is negative
The '=' holds when x and y are of same signs i.e. both are positive or both are negative
Example: |5| - |2| = |5 - 2|; |-5| - |-2| = |-5 - (-2)|; |5| - |-2| < |5 - (-2)|

Using #2 above, it can be easily seen that statement 2 is sufficient:

Since xy < 0, it must be that x and y are of opposite signs

=> |x| - |y| < |x - y|

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Intern  B
Joined: 14 Aug 2017
Posts: 24
Re: Is |x – y| > |x| – |y|? (1) y < x (2) x y < 0  [#permalink]

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Hi,
I followed the following approach to solve this question. Please correct me if I am wrong :-

Since it is DS, we need to simplify the question further if it is possible.
Is |x-y|>|x|-|y|?

Squaring both sides
Is $$(x-y)^2$$ > $$(|x|-|y|)^2$$?
On further simplifying

Is $$x^2 -2xy+y^2$$ > $$x^2-2|x||y|+y2$$?
=> Is xy>|x||y|?
=> Is xy>0?

So now we have to find out whether xy is greater than 0 or not.

Statement 1 => y<x
On re-arranging,
=> x-y>0
Now, we can take some values for x and y for which x-y is greater than 0,

let x = 2 , y= -4 => x - y = 6 > 0
$$xy = 2*(-4) = -8$$ => xy <0

let x = 4, y= 2 => x - y = 2 > 0
$$xy = 4*(2) = 8$$ => xy >0

We are not getting a definite answer from this statement. So this statement is insufficient.
We can eliminate options A and D.

Statement 2 => xy < 0
Now our simplified version of the question(Bolded Part) is that we have to find out : is xy > 0?
From this option we get that xy < 0.
We get a definite answer for the question : is xy > 0?
So this statement alone is sufficient.

Math Expert V
Joined: 02 Sep 2009
Posts: 61215
Re: Is |x – y| > |x| – |y|? (1) y < x (2) x y < 0  [#permalink]

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naju wrote:
Is $$|x – y| > |x| – |y|$$?
(1) $$y < x$$
(2) $$x y < 0$$

Discussed here: https://gmatclub.com/forum/is-x-y-x-y-1 ... 23108.html Hope it helps.

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_________________ Re: Is |x – y| > |x| – |y|? (1) y < x (2) x y < 0   [#permalink] 26 Jan 2020, 22:46
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