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

 It is currently 20 Apr 2019, 01:33

### 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

# If x+y=3 and x^2+y^2=7, then xy=?

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 7230
GMAT 1: 760 Q51 V42
GPA: 3.82
If x+y=3 and x^2+y^2=7, then xy=?  [#permalink]

### Show Tags

03 May 2017, 02:28
2
2
00:00

Difficulty:

15% (low)

Question Stats:

82% (01:06) correct 18% (02:26) wrong based on 86 sessions

### HideShow timer Statistics

If x+y=3 and $$x^2+y^2=7$$, then xy=?

A. -2
B. -1
C. 0
D. 1
E. 2

_________________
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" Intern Joined: 11 Jan 2017 Posts: 1 Re: If x+y=3 and x^2+y^2=7, then xy=? [#permalink] ### Show Tags 03 May 2017, 02:34 (x+y)^2=x^2+y^2+2xy (3)^2=7+2xy Solve to get 1 Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 7230 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: If x+y=3 and x^2+y^2=7, then xy=? [#permalink] ### Show Tags 05 May 2017, 01:50 ==> You get $$(x+y)^2=x^2+y^2+2xy$$, and if you substitute this, from $$3^2=7+2xy$$, you get 2xy=2, and xy=1. Therefore, the answer is D. 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$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"
Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 5807
Location: United States (CA)
Re: If x+y=3 and x^2+y^2=7, then xy=?  [#permalink]

### Show Tags

06 May 2017, 17:53
MathRevolution wrote:
If x+y=3 and $$x^2+y^2=7$$, then xy=?

A. -2
B. -1
C. 0
D. 1
E. 2

We are given that x + y = 3 and that x^2 + y^2 = 7. If we square both sides of x + y = 3, we will have:

x^2 + y^2 + 2xy = 9

x^2 + y^2 = 9 - 2xy

Since x^2 + y^2 = 7:

9 - 2xy = 7

-2xy = -2

xy = 1

_________________

# Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

Manager
Joined: 19 Jul 2017
Posts: 85
Location: India
Concentration: General Management, Strategy
GPA: 3.5
Re: If x+y=3 and x^2+y^2=7, then xy=?  [#permalink]

### Show Tags

28 Aug 2017, 00:17
2xy = (x+y)^2-(x^2+y^2)

xy =9-7/2=1
Hence Option D
Re: If x+y=3 and x^2+y^2=7, then xy=?   [#permalink] 28 Aug 2017, 00:17
Display posts from previous: Sort by