Register    Login    Search    Rss Feeds

 Page 1 of 1 [ 3 posts ] 



 
Author Message
 Post subject: Manhattan Question Bank Word
 Post Posted: Thu Jun 26, 2008 5:36 pm 
What is the average of x and |y| ?

(1) x + y = 20

(2) |x + y| = 20

Stacey/Ron I wanted to go over this problem with the board....You guys solve this problem by picking #s...But is it fair to rephrase it as...

If y > 0 ...(x+y)/2 =

If y < 0 ...(x-y)/2 =

So the question could be rephrased is y positive or negative to start?


Top 
 Post subject:
 Post Posted: Sun Jun 29, 2008 12:36 pm 
anyone?


Top 
 Post subject:
 Post Posted: Tue Jul 15, 2008 4:54 am 
Offline
ManhattanGMAT Staff


Posts: 7146
first off, even if you have NO CLUE how to solve this problem, you can still notice that statement (1) implies statement (2); in other words, if statement 1 is true, then statement 2 MUST be true.
this observation alone eliminates 2 answer choices: "B" (because, if 2 is sufficient, then so is 1 because it implies 2), and "C" (because the two statements together are equivalent to statement 1 by itself; statement 2 doesn't provide any new information if statement 1 is true)

so we're down to a/d/e.

try statement (1) alone:
x + y = 20

this problem has to do with POSITIVES AND NEGATIVES, because ALL problems having to do with absolute value are, at heart, about positives and negatives. therefore, you need to try both positive and negative values of y.

sample values with y positive: y = 10, x = 10
average of x and |y| = 10

sample values with y negative: y = -10, x = 30
average of x and |y| = 20

10 and 20 are different, so, insufficient
a/d are gone
answer = e


Top 
Display posts from previous:  Sort by  
 
 Page 1 of 1 [ 3 posts ] 





Who is online

Users browsing this forum: No registered users and 0 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: