Register    Login    Search    Rss Feeds

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


 Page 1 of 1 [ 5 posts ] 



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

* Tough Math problem

Author Message
GMAT Eater
 Post subject: * Tough Math problem
 Post Posted: Thu Aug 28, 2008 8:25 am 
If N and Y are positive integers and 450y=n^3, which of the following must be an integer?

Answer: Y/(3)(2^2)(5)

Can someone please explain this to me? Also, how come this particular concept is not fully explained in th "Number Properties" MGMAT book?
Top 
Rustic Myth
 Post subject:
 Post Posted: Sun Aug 31, 2008 10:23 pm 
450Y = n^3

450 =( 2*3*3*5*5)

Y = n^3 / 2 * 3^2 * 5^2

Y = {(n/2*3*5) ^ 3} * (3* 5 * 2^2)


My reasoning

As N is a integer and 450Y is equal to the third power of N, Y should have the minimum remaining prime factors of 450 to make it into a power of three. that is Y should be equal to 2*2*3*5*x*x*x.

Thus Y / 3*5*2^2 is a integer.
Top 
esledge
 Post subject: Please post question source
 Post Posted: Mon Oct 13, 2008 12:58 pm 
Offline
ManhattanGMAT Staff


Posts: 901
Location: St. Louis, MO
Please cite the source (author) of this problem. We cannot reply unless a source is cited (and, if no source is cited, we will have to delete the post!). Thanks.

Please also make sure to read and follow the forum guidelines before posting. The subject heading should be the first 5-8 words of the problem.

BTW, the Number Properties strategy guide p.15-16 discusses factors, prime boxes, and prime products. The problem can be done with that info, but please post the author of the problem first.

_________________
Emily Sledge
Instructor
ManhattanGMAT
Top 
bhuwan
 Post subject: question already answered
 Post Posted: Wed Oct 22, 2008 7:52 am 
The question appears to already have been answered:

http://www.manhattangmat.com/forums/if- ... -t279.html
Top 
RonPurewal
 Post subject:
 Post Posted: Wed Nov 05, 2008 5:09 am 
Offline
ManhattanGMAT Staff


Posts: 7146
this is a gmatprep problem, so i'm going to move this thread over to the ::ahem:: CORRECT folder.

posters: please post your problems in the correct folder. gmatprep problems have their own special little folder, so, please use it.
thanks.

here's another link:
http://www.manhattangmat.com/forums/if- ... t4311.html
Top 
Display posts from previous:  Sort by  
 
 Page 1 of 1 [ 5 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: