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Is xy > 0? (1) x – y > –5 (2) x – 2y < –7

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Is xy > 0? (1) x – y > –5 (2) x – 2y < –7 [#permalink]

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New post 24 Feb 2017, 22:10
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E

Difficulty:

  35% (medium)

Question Stats:

73% (01:46) correct 27% (01:38) wrong based on 95 sessions

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Is xy > 0?

(1) x – y > –5
(2) x – 2y < –7
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Re: Is xy > 0? (1) x – y > –5 (2) x – 2y < –7 [#permalink]

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New post 25 Feb 2017, 06:55
vikasp99 wrote:
Is xy > 0?
(1) x – y > –5
(2) x – 2y < –7



Question is asking whether x , y have equal signs .

Individually the statements are not sufficient .
Combining , statement 1 and 2 we get

-x + y < 5
x - 2y < - 7
---------------
-y < -2 = > y > 2

Substituting in one of the equation we get , x > -3
Not sufficient (x can be positive or negative) .

Answer is E .
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Re: Is xy > 0? (1) x – y > –5 (2) x – 2y < –7 [#permalink]

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New post 25 Feb 2017, 09:40
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vikasp99 wrote:
Is xy > 0?

(1) x – y > –5
(2) x – 2y < –7


Great question!

Target question: Is xy > 0

Statement 1: x – y > –5
This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several values of x and y that satisfy statement 1. Here are two:
Case a: x = 1 and y = 1, in which case xy = (1)(1) = 1. So, xy > 0
Case b: x = 1 and y = -1, in which case xy = (1)(-1) = -1. So, xy < 0
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Aside: For more on this idea of plugging in values when a statement doesn't feel sufficient, you can read my article: http://www.gmatprepnow.com/articles/dat ... lug-values

Statement 2: x – 2y < –7
There are several values of x and y that satisfy statement 1. Here are two:
Case a: x = -10 and y = -1, in which case xy = (-10)(-1) = 10. So, xy > 0
Case b: x = -10 and y = 1, in which case xy = (-10)(1) = -10. So, xy < 0
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that x – y > –5, which we can rewrite as -5 < x - y
Statement 2 tells us that x – 2y < –7
Since -7 < -5, we can COMBINE the inequalities to get: x – 2y < –7 < -5 < x - y
Focus on x – 2y < x - y
Subtract x from both sides: -2y < -y
Add 2y to both sides: 0 < y
So, y is POSITIVE, but there's no info about x.
Consider these two conflicting scenarios:
Case a: x = 2 and y = 5, in which case xy = (2)(5) = 10. So, xy > 0
Case b: x = -1 and y = 3.5, in which case xy = (-1)(3.5) = -3.5. So, xy < 0
Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

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Re: Is xy > 0? (1) x – y > –5 (2) x – 2y < –7 [#permalink]

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New post 26 Feb 2017, 04:23
GMATPrepNow wrote:

Target question: Is xy > 0

Statement 1: x – y > –5
This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several values of x and y that satisfy statement 1. Here are two:
Case a: x = 1 and y = 1, in which case xy = (1)(1) = 1. So, xy > 0
Case b: x = 1 and y = -1, in which case xy = (1)(-1) = -1. So, xy < 0
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Aside: For more on this idea of plugging in values when a statement doesn't feel sufficient, you can read my article: http://www.gmatprepnow.com/articles/dat ... lug-values

Statement 2: x – 2y < –7
There are several values of x and y that satisfy statement 1. Here are two:
Case a: x = -10 and y = -1, in which case xy = (-10)(-1) = 10. So, xy > 0
Case b: x = -10 and y = 1, in which case xy = (-10)(1) = -10. So, xy < 0
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that x – y > –5, which we can rewrite as -5 < x - y
Statement 2 tells us that x – 2y < –7
Since -7 < -5, we can COMBINE the inequalities to get: x – 2y < –7 < -5 < x - y
Focus on x – 2y < x - y
Subtract x from both sides: -2y < -y
Add 2y to both sides: 0 < y
So, y is POSITIVE, but there's no info about x.
Consider these two conflicting scenarios:
Case a: x = 2 and y = 5, in which case xy = (2)(5) = 10. So, xy > 0
Case b: x = -1 and y = 3.5, in which case xy = (-1)(3.5) = -3.5. So, xy < 0
Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

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Dear Brent,

I did it another way:

x – y > –5
x – 2y < –7 ------As both inequality have opposite sign, it is perfect for subtraction.
----------------

y>2 .........So I know 'y 'is Positive and larger than 2. No info about 'x'.. Insufficient

Answer: E

Is my reasoning valid? It gives different answer than you. Can you help please?

Thanks
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Re: Is xy > 0? (1) x – y > –5 (2) x – 2y < –7 [#permalink]

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New post 26 Feb 2017, 10:14
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Hi Mo2men,

That's perfect reasoning.

Cheers,
Brent
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Re: Is xy > 0? (1) x – y > –5 (2) x – 2y < –7 [#permalink]

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New post 08 Apr 2018, 23:40
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Re: Is xy > 0? (1) x – y > –5 (2) x – 2y < –7   [#permalink] 08 Apr 2018, 23:40
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