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

 It is currently 23 Feb 2019, 08:00

### 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

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

## Events & Promotions

###### Events & Promotions in February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar
• ### FREE Quant Workshop by e-GMAT!

February 24, 2019

February 24, 2019

07:00 AM PST

09:00 AM PST

Get personalized insights on how to achieve your Target Quant Score.
• ### Free GMAT RC Webinar

February 23, 2019

February 23, 2019

07:00 AM PST

09:00 AM PST

Learn reading strategies that can help even non-voracious reader to master GMAT RC. Saturday, February 23rd at 7 AM PT

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

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6985
GMAT 1: 760 Q51 V42
GPA: 3.82

### Show Tags

23 Feb 2017, 19:25
1
2
00:00

Difficulty:

15% (low)

Question Stats:

79% (01:00) correct 21% (01:50) wrong based on 152 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 $149 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 Joined: 19 Apr 2016 Posts: 274 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 23 Feb 2017, 19:42 1 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 CEO Joined: 11 Sep 2015 Posts: 3447 Location: Canada Re: (x+y)^2-(x-y)^2=? [#permalink] ### Show Tags 24 Feb 2017, 07:16 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 Director Joined: 06 Jan 2015 Posts: 587 Location: India Concentration: Operations, Finance GPA: 3.35 WE: Information Technology (Computer Software) Re: (x+y)^2-(x-y)^2=? [#permalink] ### Show Tags 24 Feb 2017, 09:48 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 Joined: 15 Mar 2014 Posts: 140 Location: India Concentration: Technology, General Management GPA: 3.5 WE: Operations (Telecommunications) Re: (x+y)^2-(x-y)^2=? [#permalink] ### Show Tags 25 Feb 2017, 01:02 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 Joined: 06 Jan 2015 Posts: 587 Location: India Concentration: Operations, Finance GPA: 3.35 WE: Information Technology (Computer Software) Re: (x+y)^2-(x-y)^2=? [#permalink] ### Show Tags 25 Feb 2017, 02:31 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 Joined: 16 Aug 2015 Posts: 6985 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: (x+y)^2-(x-y)^2=? [#permalink] ### Show Tags 26 Feb 2017, 20:25 ==> 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$149 for 3 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
Joined: 09 Sep 2013
Posts: 9894

### Show Tags

02 Feb 2019, 18:47
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.
_________________
Re: (x+y)^2-(x-y)^2=?   [#permalink] 02 Feb 2019, 18:47
Display posts from previous: Sort by