GMAT Changed on April 16th - Read about the latest changes here

It is currently 21 Apr 2018, 22:01

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If |x+1|=|y+1|, what is the value of x+y? 1) xy<0

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Expert Post
Math Revolution GMAT Instructor
User avatar
D
Joined: 16 Aug 2015
Posts: 5255
GMAT 1: 800 Q59 V59
GPA: 3.82
If |x+1|=|y+1|, what is the value of x+y? 1) xy<0 [#permalink]

Show Tags

New post 20 Dec 2017, 01:53
Expert's post
2
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

51% (01:26) correct 49% (01:22) wrong based on 61 sessions

HideShow timer Statistics

[GMAT math practice question]

If \(|x+1|=|y+1|\), what is the value of \(x+y\)?

1) \(xy<0\)
2) \(x>1\) and \(y<1\)
[Reveal] Spoiler: OA

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $79 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Senior Manager
Senior Manager
User avatar
S
Joined: 05 Dec 2016
Posts: 260
Concentration: Strategy, Finance
GMAT 1: 620 Q46 V29
GMAT ToolKit User
Re: If |x+1|=|y+1|, what is the value of x+y? 1) xy<0 [#permalink]

Show Tags

New post 20 Dec 2017, 05:24
opening module we get 2 outcomes:
case 1: x=y
case 2: x+y=-2
So, we need to discover whether x and y are equal or not

(1) xy<0 follows that x and y are not equal, then 2nd case applies only and x+y=-2 Sufficient
(2) x>1; y<1 we see that they are not equal, then 2nd case applies only and x+y=-2 Sufficient

Answer D
DS Forum Moderator
avatar
G
Joined: 22 Aug 2013
Posts: 1021
Location: India
Premium Member CAT Tests
Re: If |x+1|=|y+1|, what is the value of x+y? 1) xy<0 [#permalink]

Show Tags

New post 20 Dec 2017, 11:11
MathRevolution wrote:
[GMAT math practice question]

If \(|x+1|=|y+1|\), what is the value of \(x+y\)?

1) \(xy<0\)
2) \(x>1\) and \(y<1\)


When we are given that |a| = |b| (or absolute value of a is equal to absolute value of b), then there could be two cases:
Either a = b
Or a = -b

So in the given question, either x+1 = y +1 (which gives us x=y) Or x+1 = -y-1 (which gives us x+y = -2)
Now if its the first case or x=y, then we cannot find x+y (multiple values will be possible)
But if its the second case then x+y will be -2.

(1) xy < 0
If their product is less than 0 then obviously x and y have opposite signs, so they cannot be equal. So definitely we have the second case and x+y = -2. Sufficient.

(2) x > 1 and y < 1
This again tells us that x and y cannot be equal, and thus we have the second case and x+y = -2. Sufficient.

Hence D answer
Expert Post
Math Revolution GMAT Instructor
User avatar
D
Joined: 16 Aug 2015
Posts: 5255
GMAT 1: 800 Q59 V59
GPA: 3.82
Re: If |x+1|=|y+1|, what is the value of x+y? 1) xy<0 [#permalink]

Show Tags

New post 21 Dec 2017, 00:38
=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question, and then recheck the question

Modifying the original condition gives:

\(|x+1|=|y+1|\)
\(⇔ (x+1)^2=(y+1)^2\)
\(⇔ (x+1)^2=(y+1)^2\)
\(⇔ (x+1)^2-(y+1)2=0\)
\(⇔ (x+1+y+1)(x+1-y-1)=0\)
\(⇔ (x+y+2)(x-y)=0\)
\(⇔ x+y=-2\) or \(x=y\)

As we have 2 variables (x and y) and 1 equation in the original condition, D is most likely to be the answer.

Condition 1)
Since \(xy < 0, x≠y.\)
So, \(x + y = -2\), and condition 1) is sufficient.

Condition 2)
Since \(x>1\) and \(y<1, x≠y.\)
So, \(x + y = -2\).
Condition 2) is sufficient too.

Therefore, the answer is D.

Note: Since conditions 1) and 2) are similar, D is most likely to be the answer by Tip 1).

Answer: D
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $79 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Re: If |x+1|=|y+1|, what is the value of x+y? 1) xy<0   [#permalink] 21 Dec 2017, 00:38
Display posts from previous: Sort by

If |x+1|=|y+1|, what is the value of x+y? 1) xy<0

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.