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

 It is currently 19 Sep 2018, 02:56

### 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

# For all numbers x and y, the operationΦ is defined by x?y = (x + y)(x

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 49254
For all numbers x and y, the operationΦ is defined by x?y = (x + y)(x  [#permalink]

### Show Tags

21 Aug 2018, 06:24
00:00

Difficulty:

15% (low)

Question Stats:

91% (01:09) correct 9% (01:13) wrong based on 23 sessions

### HideShow timer Statistics

For all numbers x and y, the operation ? is defined by x?y = (x + y)(x - y) + (y - x)(y + x) + xy. What is the value of $$\sqrt{12}?\sqrt{3}$$?

A. 6
B. 12
C. 18
D. 24
E. 36

_________________
Manager
Joined: 18 Jul 2018
Posts: 188
Location: India
Concentration: Finance, Marketing
WE: Engineering (Energy and Utilities)
For all numbers x and y, the operationΦ is defined by x?y = (x + y)(x  [#permalink]

### Show Tags

21 Aug 2018, 06:32
Given x?y = (x + y)(x - y) + (y - x)(y + x) + xy
x = $$\sqrt{12}$$
y = $$\sqrt{3}$$
x?y = ($$x^2$$-$$y^2$$) + ($$y^2$$-$$x^2$$) + $$\sqrt{12}$$*$$\sqrt{3}$$
= 12-3 + 3-12 + $$\sqrt{36}$$
= 6

PS Forum Moderator
Joined: 25 Feb 2013
Posts: 1213
Location: India
GPA: 3.82
Re: For all numbers x and y, the operationΦ is defined by x?y = (x + y)(x  [#permalink]

### Show Tags

21 Aug 2018, 06:33
Bunuel wrote:
For all numbers x and y, the operation ? is defined by x?y = (x + y)(x - y) + (y - x)(y + x) + xy. What is the value of $$\sqrt{12}?\sqrt{3}$$?

A. 6
B. 12
C. 18
D. 24
E. 36

$$x?y = (x + y)(x - y) + (y - x)(y + x) + xy$$

$$=>x?y=x^2-y^2+y^2-x^2+xy=xy$$

$$\sqrt{12}?\sqrt{3}=\sqrt{12*3}=6$$

Option A
Re: For all numbers x and y, the operationΦ is defined by x?y = (x + y)(x &nbs [#permalink] 21 Aug 2018, 06:33
Display posts from previous: Sort by

# Events & Promotions

 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®.