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

It is currently 17 Oct 2019, 13:29

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

If xy = 7 and x – y = 7, then x² +

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

Hide Tags

Find Similar Topics 
GMAT Club Legend
GMAT Club Legend
User avatar
V
Joined: 12 Sep 2015
Posts: 4007
Location: Canada
If xy = 7 and x – y = 7, then x² +  [#permalink]

Show Tags

New post 17 Feb 2017, 09:55
3
Top Contributor
11
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

65% (01:21) correct 35% (01:56) wrong based on 193 sessions

HideShow timer Statistics

If xy = 7 and x – y = 7, then x² + y² =

(A) 35
(B) 42
(C) 49
(D) 56
(E) 63

* Kudos for all correct solutions

_________________
Test confidently with gmatprepnow.com
Image
Most Helpful Expert Reply
GMAT Club Legend
GMAT Club Legend
User avatar
V
Joined: 12 Sep 2015
Posts: 4007
Location: Canada
Re: If xy = 7 and x – y = 7, then x² +  [#permalink]

Show Tags

New post 22 Mar 2017, 14:43
3
Top Contributor
2
GMATPrepNow wrote:
If xy = 7 and x – y = 7, then x² + y² =

(A) 35
(B) 42
(C) 49
(D) 56
(E) 63


The important thing to recognize here is that if we square (x - y), we get a x² term and a y² term. We also get an extra xy term, but that's okay, because we're given some information about the product xy.

So, take: x – y = 7 and...
Square both sides: (x - y)² = 7²
Expand: x² - 2xy + y² = 49
Since we're told xy = 7, we'll replace xy with 7 to get: x² - 2(7) + y² = 49
Simplify: x² - 14 + y² = 49
Add 14 to both sides: x² + y² = 63

Answer: E

RELATED VIDEO

_________________
Test confidently with gmatprepnow.com
Image
Most Helpful Community Reply
Intern
Intern
avatar
B
Joined: 08 Aug 2016
Posts: 18
GMAT ToolKit User
Re: If xy = 7 and x – y = 7, then x² +  [#permalink]

Show Tags

New post 17 Feb 2017, 10:13
4
1
(x-y)^2= x^2 + y^2 - 2xy
7^2 = x^2 + y^2 -2*7
x^2 + y^2 = 49+14
x^2 + y^2 = 63

Sent from my Redmi Note 3 using GMAT Club Forum mobile app
_________________
कर्मणयेवाधिकारस्ते मा फलेषु कदाचन|
General Discussion
VP
VP
User avatar
V
Joined: 23 Feb 2015
Posts: 1257
GMAT ToolKit User Premium Member
Re: If xy = 7 and x – y = 7, then x² +  [#permalink]

Show Tags

New post 22 Mar 2017, 18:34
GMATPrepNow wrote:
If xy = 7 and x – y = 7, then x² + y² =

(A) 35
(B) 42
(C) 49
(D) 56
(E) 63

* Kudos for all correct solutions

x² + y²=(x-y)²+2xy
=7²+2*7
=49+14
=63
So, the correct choice is
_________________
“The heights by great men reached and kept were not attained in sudden flight but, they while their companions slept, they were toiling upwards in the night.”
Henry Wadsworth Longfellow

Do you need official questions for Quant?
3700 Unique Official GMAT Quant Questions
------
SEARCH FOR ALL TAGS
GMAT Club Tests
Board of Directors
User avatar
D
Status: QA & VA Forum Moderator
Joined: 11 Jun 2011
Posts: 4776
Location: India
GPA: 3.5
WE: Business Development (Commercial Banking)
GMAT ToolKit User
Re: If xy = 7 and x – y = 7, then x² +  [#permalink]

Show Tags

New post 23 Mar 2017, 08:47
GMATPrepNow wrote:
If xy = 7 and x – y = 7, then x² + y² =

(A) 35
(B) 42
(C) 49
(D) 56
(E) 63

* Kudos for all correct solutions


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

Or, \(7^2 + 2*7 = x^2 + y^2\)

Or, \(49 + 14 = x^2 + y^2\)

Or, \(x^2 + y^2 = 63\)

Thus, answer must be (E) 63...
_________________
Thanks and Regards

Abhishek....

PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS

How to use Search Function in GMAT Club | Rules for Posting in QA forum | Writing Mathematical Formulas |Rules for Posting in VA forum | Request Expert's Reply ( VA Forum Only )
Retired Moderator
User avatar
P
Joined: 19 Mar 2014
Posts: 922
Location: India
Concentration: Finance, Entrepreneurship
GPA: 3.5
GMAT ToolKit User
Re: If xy = 7 and x – y = 7, then x² +  [#permalink]

Show Tags

New post 16 Jul 2017, 13:09
If xy = 7 and x – y = 7, then x² + y² =

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

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

\(x^2 + y^2 = (7)^2 + 2 * 7\)

\(x^2 + y^2 = 49 + 14\)

\(x^2 + y^2 = 63\)

Hence, Answer is E

Did you like the answer? 1 Kudos Please :good
_________________
"Nothing in this world can take the place of persistence. Talent will not: nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not: the world is full of educated derelicts. Persistence and determination alone are omnipotent."

Best AWA Template: https://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html#p470475
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 13243
Re: If xy = 7 and x – y = 7, then x² +  [#permalink]

Show Tags

New post 19 Sep 2019, 07:16
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: If xy = 7 and x – y = 7, then x² +   [#permalink] 19 Sep 2019, 07:16
Display posts from previous: Sort by

If xy = 7 and x – y = 7, then x² +

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





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