• Board contributors include instructors with "800" GMAT scores.
  • 95% of posts have replies within 24 hours.
  • Join for discounts with 800score, VeritasPrep and ManhattanGMAT


FAQ  - Register  - Search - Login 

All times are UTC - 7 hours




Post new topic Reply to topic  [ 2 posts ] 
Author Message
 Post subject: GMAT Symbols
PostPosted: Mon May 13, 2013 9:51 am 
Offline
User avatar

Joined: Tue Apr 13, 2010 8:48 am
Posts: 477
If x # y = 3x² – y and x @ y = x + 2y, which of the following is equal to 2x # (2x @ y)?

A. 2x² + 8xy + 4y²
B. -x² + 8x – 4y
C. 10x² – 8 – 4y
D. 8x² – 4y²
E. 12x² – 2x – 2y

(E) Recall from the rules of order of operations (PEMDAS), that we always work with what is in parenthesis first. Essentially, we want to work from the inside out with this problem.

2x # (2x @ y) = 2x # (2x + 2y) = 3(2x)² – (2x + 2y) = 12x² – 2x – 2y.

The correct answer is E.
----------

How do you derive "12x²..." in answer choice E? Shouldn't it be "6x²..."?


Top
 Profile  
 
 Post subject: Re: GMAT Symbols
PostPosted: Mon May 13, 2013 9:52 am 
Offline
User avatar

Joined: Fri Apr 09, 2010 2:11 pm
Posts: 453
Quote:
2x # (2x @ y) = 2x # (2x + 2y) = 3(2x)² – (2x + 2y) = 12x² – 2x – 2y

Let's write the calculations in details:
1. 2x # (2x @ y) =

We apply the definition of the operation "@" to 2x and y.
2x @ y = (2x) + 2y = 2x + 2y

2. 2x # (2x @ y) = 2x # (2x + 2y) =

We use the definition of the operation "#" for 2x and (2x + 2y).
2x # (2x + 2y) = 3(2x)² – (2x + 2y) = 3 × 2² × x² – 2x – 2y
3 × 2² = 3 × 4 = 12

Therefore
2x # (2x @ y) = 2x # (2x + 2y) = 12x² – 2x – 2y


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 2 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Template made by DEVPPL -
phpBB SEO
 
GMAT(TM) and GMAT CAT (TM) are registered trademarks of the Graduate Management Admission Council(TM). The Graduate Management Admission Council(TM) does not endorse, nor is affiliated in any way with the owner or any content of this site.