GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 21 Oct 2019, 09:12

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

(x+y)^2-(x-y)^2=?

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

Hide Tags

Find Similar Topics 
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 8025
GMAT 1: 760 Q51 V42
GPA: 3.82
(x+y)^2-(x-y)^2=?  [#permalink]

Show Tags

New post 23 Feb 2017, 20:25
1
3
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

76% (01:00) correct 24% (01:45) wrong based on 191 sessions

HideShow timer Statistics

\((x+y)^2-(x-y)^2=?\)

1) xy=5
2) x+y=6

_________________
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 1 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
G
Joined: 19 Apr 2016
Posts: 268
Location: India
GMAT 1: 570 Q48 V22
GMAT 2: 640 Q49 V28
GPA: 3.5
WE: Web Development (Computer Software)
Re: (x+y)^2-(x-y)^2=?  [#permalink]

Show Tags

New post 23 Feb 2017, 20:42
2
MathRevolution wrote:
\((x+y)^2-(x-y)^2=?\)

1) xy=5
2) x+y=6


\((x+y)^2-(x-y)^2\)
\(=x^2+y^2+2xy-x^2-y^2+2xy\)
\(=4xy\)

St I
xy=5 ==> 4*xy = 4*5 = 20 ----------Sufficient

St II
x+y=6, we have no information about x-y ----------Insufficient

Hence Option A is correct
Hit Kudos if you liked it 8-)
GMAT Club Legend
GMAT Club Legend
User avatar
V
Joined: 12 Sep 2015
Posts: 4015
Location: Canada
Re: (x+y)^2-(x-y)^2=?  [#permalink]

Show Tags

New post 24 Feb 2017, 08:16
Top Contributor
MathRevolution wrote:
\((x+y)^2-(x-y)^2 =?\)

1) xy = 5
2) x + y = 6


Target question: What is the value of (x+y)² - (x-y)² ?

This is a good candidate for rephrasing the target question.
(x+y)² - (x-y)² = [x² + 2xy + y²] - [x² - 2xy + y²]
= 4xy


REPHRASED target question: What is the value of 4xy?

Statement 1: xy = 5
If xy = 5, then 4xy = 4(5) = 20
Since we can answer the REPHRASED target question with certainty, statement 1 is SUFFICIENT

Statement 2: x + y = 6
There are several values of x and y that satisfy statement 2. Here are two:
Case a: x = 0 and y = 6 in which case, 4xy = 4(0)(6) = 0
Case b: x = 1 and y = 5 in which case, 4xy = 4(1)(5) = 20
Since we cannot answer the REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT

Answer: A

RELATED VIDEOS FROM OUR COURSE




_________________
Test confidently with gmatprepnow.com
Image
Director
Director
User avatar
V
Joined: 06 Jan 2015
Posts: 689
Location: India
Concentration: Operations, Finance
GPA: 3.35
WE: Information Technology (Computer Software)
Re: (x+y)^2-(x-y)^2=?  [#permalink]

Show Tags

New post 24 Feb 2017, 10:48
MathRevolution wrote:
\((x+y)^2-(x-y)^2=?\)

1) xy=5
2) x+y=6


\((x+y)^2-(x-y)^2==>4xy=?\)

1)x+y=5 hence 4xy==>20 -- Suff

2) x+y=6--Insuff as we don't know the value of x-y.

Hence A
_________________
आत्मनॊ मोक्षार्थम् जगद्धिताय च

Resource: GMATPrep RCs With Solution
Manager
Manager
User avatar
G
Joined: 15 Mar 2014
Posts: 141
Location: Singapore
Concentration: Technology, General Management
GPA: 3.5
WE: Operations (Telecommunications)
Re: (x+y)^2-(x-y)^2=?  [#permalink]

Show Tags

New post 25 Feb 2017, 02:02
1
NandishSS wrote:

2) x+y=6--Insuff as we don't know the value of x-y.

Hence A


I don't think we can eliminate that answer choice just 'cause the value of (x-y) is unknown. Rather it should be because the simplied xy is unknown. Just my way of thinking :)
_________________
Hit +1 Kudos If you like my post! :)
Director
Director
User avatar
V
Joined: 06 Jan 2015
Posts: 689
Location: India
Concentration: Operations, Finance
GPA: 3.35
WE: Information Technology (Computer Software)
Re: (x+y)^2-(x-y)^2=?  [#permalink]

Show Tags

New post 25 Feb 2017, 03:31
ashwink wrote:
NandishSS wrote:

2) x+y=6--Insuff as we don't know the value of x-y.

Hence A


I don't think we can eliminate that answer choice just 'cause the value of (x-y) is unknown. Rather it should be because the simplied xy is unknown. Just my way of thinking :)


Hi ashwink,

You are right, however here we know x+y don't know about x-y. x-y can be anything...4xy comes only after simplification....if we know x-y as well then ans would be B also. :-)

Happy Prepping!!!
_________________
आत्मनॊ मोक्षार्थम् जगद्धिताय च

Resource: GMATPrep RCs With Solution
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 8025
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: (x+y)^2-(x-y)^2=?  [#permalink]

Show Tags

New post 26 Feb 2017, 21:25
==> If you modify the original condition and the question, \((x+y)^2-(x-y)^2=?\) becomes (x+y-x+y)(x+y+x-y)=?, and if you simplify this, you get (2y)(2x)=?, 4xy=?. Thus, for con 1), you get xy=5, hence it is unique and sufficient.

The answer is A.
Answer: A
_________________
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 1 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 13370
Re: (x+y)^2-(x-y)^2=?  [#permalink]

Show Tags

New post 02 Feb 2019, 19:47
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
GMAT Club Bot
Re: (x+y)^2-(x-y)^2=?   [#permalink] 02 Feb 2019, 19:47
Display posts from previous: Sort by

(x+y)^2-(x-y)^2=?

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





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