Register    Login    Search    Rss Feeds

 Page 1 of 1 [ 6 posts ] 



 
Author Message
 Post subject: Is |xy|> (xy)^2
 Post Posted: Wed May 30, 2012 10:54 pm 
Offline
Forum Guests


Posts: 2
Is |xy|> (xy)^2 ?

1. 0<x^2<1/4
2. 0<y^2<1/9

The OA is C. I don't quite understand why its C and not D.


Top 
 Post subject: Re: Is |xy|> (xy)^2
 Post Posted: Thu May 31, 2012 7:29 am 
Offline
ManhattanGMAT Staff


Posts: 8179
uzair_baig wrote:
Is |xy|> (xy)^2 ?

1. 0<x^2<1/4
2. 0<y^2<1/9

The OA is C. I don't quite understand why its C and not D.


the left-hand side is the square root of the right-hand side. i.e., |xy| is the square root of (xy)^2.

so, a YES to this question means that, when |xy| is squared, it gets smaller.
if |xy| is between 0 and 1, the answer to the question will be YES.

the individual statements aren't sufficient because they don't impose any constraints at all on the other number.
for instance, statement (1) limits x to between 0 and 1/2 (or between -1/2 and 0) -- but, under that statement, y can be literally any number in the world.
so, if x is, say, 1/4 and y is another fraction, you're going to get a YES to the question.
but, if x is 1/4 and y is 1,000,000,000, then you're going to get a NO to the question.

same logic applies to the other statement, with the roles of x and y reversed.

once you get the two statements together, though, you know for sure that both x and y are fractions. this way |xy| is definitely less than 1, and so it will definitely get smaller when you square it.

_________________
Being well-dressed gives a feeling of inward tranquillity [that] religion is powerless to bestow.
C.F. Forbes


Top 
 Post subject: Re: Is |xy|> (xy)^2
 Post Posted: Sun Jul 01, 2012 11:41 pm 
Offline
Students


Posts: 16
Greetings Ron,

I just wanted to clarify one doubt here. The question hasn't mentioned that x and y are different. Even combining (1) and (2), if we consider
x^2 = 1/25 (1/25<1/4). So x may be (+/- 1/5). Similarly if we consider y^2 = 1/25 (1/25< 1/9). So (y may be +/- 1/5).
Irrespective of the signs if we consider (since both sides are going to be positive anyways), we would get

|x.y| !> (x.y)^2

I know if this is a GMAT Prep question, then it's preposterous to question the correct answer. But if I would have got this question, I would have marked it (E) : (
Am I missing something here : (

Thanks
Prashant
An ardent fan of RON :) ...


Top 
 Post subject: Re: Is |xy|> (xy)^2
 Post Posted: Mon Jul 02, 2012 6:40 pm 
Offline
ManhattanGMAT Staff


Posts: 8179
prashant.ranjan wrote:
Greetings Ron,

I just wanted to clarify one doubt here. The question hasn't mentioned that x and y are different. Even combining (1) and (2), if we consider
x^2 = 1/25 (1/25<1/4). So x may be (+/- 1/5). Similarly if we consider y^2 = 1/25 (1/25< 1/9). So (y may be +/- 1/5).
Irrespective of the signs if we consider (since both sides are going to be positive anyways), we would get

|x.y| !> (x.y)^2


try again.
with your choice of numbers, |xy| is 1/25, but (xy)^2 is (1/25)^2, which is a lot smaller.

_________________
Being well-dressed gives a feeling of inward tranquillity [that] religion is powerless to bestow.
C.F. Forbes


Top 
 Post subject: Re: Is |xy|> (xy)^2
 Post Posted: Tue Jul 03, 2012 12:56 pm 
Offline
Students


Posts: 16
Gosh!!!!!!
What i was thinking :P
Srry to take up your time..

Thanks and Regards
Prashant


Top 
 Post subject: Re: Is |xy|> (xy)^2
 Post Posted: Thu Jul 05, 2012 5:25 am 
Offline
ManhattanGMAT Staff


Posts: 4462
Location: Southwest Airlines, seat 21C
:)

_________________
Tim Sanders
Manhattan GMAT Instructor


Top 
Display posts from previous:  Sort by  
 
 Page 1 of 1 [ 6 posts ] 





Who is online

Users browsing this forum: No registered users and 1 guest

 
 

 
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