Register    Login    Search    Rss Feeds

Forums Home » Ask An Instructor » GMAT Math » GMAT Prep Math


 Page 1 of 1 [ 2 posts ] 



  Print view Print view Previous topic Previous topic | Next topic Next topic
 

MGMAT CAT#1:Exponents/Algebra

Author Message
afvatcha
 Post subject: MGMAT CAT#1:Exponents/Algebra
 Post Posted: Wed Dec 02, 2009 12:20 am 
Offline
Course Students


Posts: 34
Hi, I came across this data suff. in the MGMAT CAT#1.

8a(1/4)b = ?

(1) b = 1.5a
(2) a = 2

The correct answer is (A).

I understand why (A) is sufficient, but why isn't (B). The explanation says 3a-2b. So we can plug in A and set 3a-2b to 0. Well why can't you do that for (B)?
Top 
Ben Ku
 Post subject: Re: MGMAT CAT#1:Exponents/Algebra
 Post Posted: Thu Dec 24, 2009 7:02 pm 
Offline
ManhattanGMAT Staff


Posts: 823
Please be clear when re-typing the problem. This problem is actually:

(8^a)*(1/4)^b = ?

To do this problem, we can simplify this expression so everything has the same base.

(2^3)^a * (2^-2)^b
= 2^3a * 2^-2b
= 2^(3a - 2b)

The question is REALLY asking for "What is 3a - 2b?".

Statement (1) is sufficient, because if b = 1.5a, then 3a - 2b = 3a - 2(1.5a) = 3a - 3a = 0.

Hope that helps.

_________________
Ben Ku
Instructor
ManhattanGMAT
Top 
Display posts from previous:  Sort by  
 
 Page 1 of 1 [ 2 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: