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If x and y are integers, and x + y < 0, is x — y > 0

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If x and y are integers, and x + y < 0, is x — y > 0  [#permalink]

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New post 08 Apr 2018, 09:41
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If x and y are integers, and x + y < 0, is x — y > 0?

1) |x| + |y| > |x|
2) x^y = 1

The OA solution suggested testing cases ....Any suggestions on doing this via logic or critical thinking ?
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If x and y are integers, and x + y < 0, is x — y > 0  [#permalink]

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New post 08 Apr 2018, 11:50
hmm if interested in testing cases -- here is the link to the OA.....you should be able to find it using test cases ...but it takes too long imo

Has to be a simpler way

https://www.manhattanprep.com/gmat/blog ... flowchart/
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If x and y are integers, and x + y < 0, is x — y > 0  [#permalink]

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New post 08 Apr 2018, 12:13
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1
jabhatta@umail.iu.edu wrote:
If x and y are integers, and x + y < 0, is x — y > 0?

1) |x| + |y| > |x|
2) x^y = 1

The OA solution suggested testing cases ....Any suggestions on doing this via logic or critical thinking ?


If x and y are integers, and x + y < 0, is x — y > 0?

Notice that the question asks whether x > y.


(1) |x| + |y| > |x|. Cancel |x| on both sides: |y| > 0. Since an absolute value of a number is always more than or equal to 0, then this statement is simply telling us that y ≠ 0. Not sufficient.


(2) x^y = 1. This could be true in three cases:

a. y = 0 and x = any non-zero integer;
b. x = -1 and y = even.
c. x = 1 and y = any integer.

We can have cases satisfying the above and x + y < 0 and giving different answers to the question whether x > y. For example, y = 0 and x = -1 or y = -2 and x = -1. Not sufficient.

(1)+(2) Since (1) rules out y ≠ 0, then we are left with cases b and c from (2):

b. x = -1 and y = even.. This and x + y < 0 to be true y should be negative even number: -2, -4, ... In all these cases x > y.
c. x = 1 and y = any integer. This and x + y < 0 to be true y should be less than -1: -2, -3, -4, ... In all these cases x > y.

In all possible cases we got an YES answer to the question. Sufficient.


Answer: C.

Hope it's clear.
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Collection of Questions:
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DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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If x and y are integers, and x + y < 0, is x — y > 0  [#permalink]

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New post Updated on: 08 Apr 2018, 12:33
Bunuel wrote:
jabhatta@umail.iu.edu wrote:
If x and y are integers, and x + y < 0, is x — y > 0?

1) |x| + |y| > |x|
2) x^y = 1

The OA solution suggested testing cases ....Any suggestions on doing this via logic or critical thinking ?


If x and y are integers, and x + y < 0, is x — y > 0?

Notice that the question asks whether x > y.


(1) |x| + |y| > |x|. Cancel |x| on both sides: |y| > 0. Since an absolute value of a number is always more than or equal to 0, then this statement is simply telling us that y ≠ 0. Not sufficient.


(2) x^y = 1. This could be true in three cases:

a. y = 0 and x = any non-zero integer;
b. x = -1 and y = even.
c. x = 1 and y = any integer.

We can have cases satisfying the above and x + y < 0 and giving different answers to the question whether x > y. For example, y = 0 and x = -1 or y = -2 and x = -1. Not sufficient.

(1)+(2) Since (1) rules out y ≠ 0, then we are left with cases b and c from (2):

b. x = -1 and y = even.. This and x + y < 0 to be true y should be negative even number: -2, -4, ... In all these cases x > y.
c. x = 1 and y = any integer. This and x + y < 0 to be true y should be less than -1: -2, -3, -4, ... In all these cases x > y.

In all possible cases we got an YES answer to the question. Sufficient.


Answer: C.

Hope it's clear.


Wow -- this is really well done ..

Bunuel - do you think its easier to

a) test cases in this case or
b) do you prefer arithmetic

Do you think you could have done your method in 3 mins time pressure ?

Originally posted by jabhatta@umail.iu.edu on 08 Apr 2018, 12:30.
Last edited by jabhatta@umail.iu.edu on 08 Apr 2018, 12:33, edited 1 time in total.
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Re: If x and y are integers, and x + y < 0, is x — y > 0  [#permalink]

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New post 08 Apr 2018, 12:32
Bunuel wrote:
jabhatta@umail.iu.edu wrote:
If x and y are integers, and x + y < 0, is x — y > 0?

1) |x| + |y| > |x|
2) x^y = 1

The OA solution suggested testing cases ....Any suggestions on doing this via logic or critical thinking ?


If x and y are integers, and x + y < 0, is x — y > 0?

Notice that the question asks whether x > y.


(1) |x| + |y| > |x|. Cancel |x| on both sides: |y| > 0. Since an absolute value of a number is always more than or equal to 0, then this statement is simply telling us that y ≠ 0. Not sufficient.


(2) x^y = 1. This could be true in three cases:

a. y = 0 and x = any non-zero integer;
b. x = -1 and y = even.
c. x = 1 and y = any integer.

We can have cases satisfying the above and x + y < 0 and giving different answers to the question whether x > y. For example, y = 0 and x = -1 or y = -2 and x = -1. Not sufficient.

(1)+(2) Since (1) rules out y ≠ 0, then we are left with cases b and c from (2):

b. x = -1 and y = even.. This and x + y < 0 to be true y should be negative even number: -2, -4, ... In all these cases x > y.
c. x = 1 and y = any integer. This and x + y < 0 to be true y should be less than -1: -2, -3, -4, ... In all these cases x > y.


In all possible cases we got an YES answer to the question. Sufficient.


Answer: C.

Hope it's clear.


Hi Bunuel - a question on the highlighted portion (bullet b and c)

How is it bullet B tells us x = -1 whereas bullet c tells us x = 1

Dont bullet b and bullet C almost contradict each other in a way ?
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Re: If x and y are integers, and x + y < 0, is x — y > 0  [#permalink]

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New post 08 Apr 2018, 12:34
jabhatta@umail.iu.edu wrote:
Bunuel wrote:
jabhatta@umail.iu.edu wrote:
If x and y are integers, and x + y < 0, is x — y > 0?

1) |x| + |y| > |x|
2) x^y = 1

The OA solution suggested testing cases ....Any suggestions on doing this via logic or critical thinking ?


If x and y are integers, and x + y < 0, is x — y > 0?

Notice that the question asks whether x > y.


(1) |x| + |y| > |x|. Cancel |x| on both sides: |y| > 0. Since an absolute value of a number is always more than or equal to 0, then this statement is simply telling us that y ≠ 0. Not sufficient.


(2) x^y = 1. This could be true in three cases:

a. y = 0 and x = any non-zero integer;
b. x = -1 and y = even.
c. x = 1 and y = any integer.

We can have cases satisfying the above and x + y < 0 and giving different answers to the question whether x > y. For example, y = 0 and x = -1 or y = -2 and x = -1. Not sufficient.

(1)+(2) Since (1) rules out y ≠ 0, then we are left with cases b and c from (2):

b. x = -1 and y = even.. This and x + y < 0 to be true y should be negative even number: -2, -4, ... In all these cases x > y.
c. x = 1 and y = any integer. This and x + y < 0 to be true y should be less than -1: -2, -3, -4, ... In all these cases x > y.

In all possible cases we got an YES answer to the question. Sufficient.


Answer: C.

Hope it's clear.


Wow -- this is really well done ..

Bunuel - do you think its easier to

a) test cases in this case or
b) do you prefer your method in terms -- Do you think you could have done your method in 3 mins


I'd done this way but it's really subjective.
_________________

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Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Math Expert
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Joined: 02 Sep 2009
Posts: 50000
Re: If x and y are integers, and x + y < 0, is x — y > 0  [#permalink]

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New post 08 Apr 2018, 12:38
jabhatta@umail.iu.edu wrote:
Bunuel wrote:
jabhatta@umail.iu.edu wrote:
If x and y are integers, and x + y < 0, is x — y > 0?

1) |x| + |y| > |x|
2) x^y = 1

The OA solution suggested testing cases ....Any suggestions on doing this via logic or critical thinking ?


If x and y are integers, and x + y < 0, is x — y > 0?

Notice that the question asks whether x > y.


(1) |x| + |y| > |x|. Cancel |x| on both sides: |y| > 0. Since an absolute value of a number is always more than or equal to 0, then this statement is simply telling us that y ≠ 0. Not sufficient.


(2) x^y = 1. This could be true in three cases:

a. y = 0 and x = any non-zero integer;
b. x = -1 and y = even.
c. x = 1 and y = any integer.

We can have cases satisfying the above and x + y < 0 and giving different answers to the question whether x > y. For example, y = 0 and x = -1 or y = -2 and x = -1. Not sufficient.

(1)+(2) Since (1) rules out y ≠ 0, then we are left with cases b and c from (2):

b. x = -1 and y = even.. This and x + y < 0 to be true y should be negative even number: -2, -4, ... In all these cases x > y.
c. x = 1 and y = any integer. This and x + y < 0 to be true y should be less than -1: -2, -3, -4, ... In all these cases x > y.


In all possible cases we got an YES answer to the question. Sufficient.


Answer: C.

Hope it's clear.


Hi Bunuel - a question on the highlighted portion (bullet b and c)

How is it bullet B tells us x = -1 whereas bullet c tells us x = 1

Dont bullet b and bullet C almost contradict each other in a way ?


Those are different cases for which x^y = 1:
b. x = -1 and y = even. For example, x= -1 and y = 2 --> x^y = 1.
c. x = 1 and y = any integer. For example, x= 1 and y = 3 --> x^y = 1.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

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Re: If x and y are integers, and x + y < 0, is x — y > 0  [#permalink]

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New post 10 Apr 2018, 05:54
jabhatta@umail.iu.edu wrote:
If x and y are integers, and x + y < 0, is x — y > 0?

1) |x| + |y| > |x|
2) x^y = 1

The OA solution suggested testing cases ....Any suggestions on doing this via logic or critical thinking ?


You can imagine the numbers on the number line to solve it.

x and y are integers.

x + y < 0 implies at least one of x and y is negative and if there is one negative number and one positive, the negative one has higher absolute value. I imagine them placed on the number line.

Question: Is x - y > 0
This just means: "Is x to the right of y on the number line?"

1) |x| + |y| > |x|
If absolute value of the two is greater than the absolute value of x alone, it just means that y is not 0.
Not sufficient

2) x^y = 1
This can be done in 2 main ways: Either make y = 0 or make x = 1 (with y as any integer) / -1 (with y even)
If y is 0, x must be negative and answer would be "No"
If x = 1, y must be negative and answer would be "Yes"
Not sufficient

Using both statements, x = 1 (with y as any integer) / -1 (with y even)
If x is 1, answer is "Yes"
If x = -1, y is even. So y is one of -2, -4, -6 etc in which case answer is "Yes". y cannot be positive because the negative value must have higher absolute value.
Sufficient

Answer (C)
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Re: If x and y are integers, and x + y < 0, is x — y > 0 &nbs [#permalink] 10 Apr 2018, 05:54
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