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NUMBER PROP DS

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 Post subject: NUMBER PROP DS
 Post Posted: Thu Sep 25, 2008 6:03 pm 
If n and y are +ve integers and 450y=n^3, then which of the following must be an even integer ?

1) y / (3)(2^2)(5)

2) y / (3^2)(2)(5)

3) y / (3)(2)(5^2)

A)None
B)1 only
C) 2 only
D) 3 only
E) 1,2 and 3.

I tried by making y=n^3/450 and then prime factorising 450. In which case, 2 and 3 seem better. But thats not the answer. Grateful if anyone has any pointers.
Top 
Kunal
 Post subject:
 Post Posted: Thu Sep 25, 2008 11:07 pm 
I would say the answer is A.None.

The question is looking for even integers. by the method you described we can say 2 & 3 are integers. But since options 2 and 3 is divided by 2 we cannot guarantee the result is even! what say?
Top 
drsbasu
 Post subject: num prop
 Post Posted: Sat Sep 27, 2008 6:45 am 
Nope thats not the answer. Ron sent me this question a few months ago - and its quite hard actually.

Ron if you`re here - can you explain this ?

Ta
Shamik.
Top 
divya
 Post subject:
 Post Posted: Tue Sep 30, 2008 8:52 pm 
Posted: Thu Sep 25, 2008 5:03 pm Post subject: NUMBER PROP DS

--------------------------------------------------------------------------------

If n and y are +ve integers and 450y=n^3, then which of the following must be an even integer ?

1) y / (3)(2^2)(5)

2) y / (3^2)(2)(5)

3) y / (3)(2)(5^2)

A)None
B)1 only
C) 2 only
D) 3 only
E) 1,2 and 3.

obtain all prime factors of 450 = 5x5x3x3x2
Therefore 5x5x3x3x2 x y = n^3
in order to make the right hand side a cube, we are missing one 5, one 3, and two 2s in order to make it a perfect cube

thus y/ (3)(5) (2 ^ 2) should be an integer
Therefore answer: B
Top 
Kunal
 Post subject:
 Post Posted: Wed Oct 01, 2008 12:27 am 
Would that work out to an even int or just an int?
Top 
divya
 Post subject:
 Post Posted: Tue Oct 07, 2008 7:59 pm 
I think in the GMAT Prep test, the question asks whether it is an integer.

Exact question uploaded.
Top 
divya
 Post subject:
 Post Posted: Tue Oct 07, 2008 8:05 pm 
exact GMATPrep question attached.
Image
Top 
divya
 Post subject:
 Post Posted: Tue Oct 07, 2008 8:09 pm 
additionally if the question was whether it is an even integer, I would still choose i. as 3 * 2 ^2 * 5 = 60 and Y has to be an even integer to be divisble by 60.

so for example, 60, 120, 180, 240 etc.
Top 
RonPurewal
 Post subject:
 Post Posted: Fri Oct 24, 2008 4:45 am 
Offline
ManhattanGMAT Staff


Posts: 7146
http://www.manhattangmat.com/forums/if- ... t4311.html

http://www.manhattangmat.com/forums/if- ... -t279.html

people!
"450y" is the world's greatest search term. type it into the box and watch at least 3 old threads come up.

i understand that the search box is mediocre at best, especially when the search string contains rather generic terms (lots of math problems don't really contain anything other than numbers and letters, making searches difficult), but, come on, people. you should find this one.
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