NUMBER PROP DS

[guest]

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.

[Kunal]

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?

[drsbasu]

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.

[divya]

Posted: Thu Sep 25, 2008 5:03 pm Post subject: NUMBER PROP DS

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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

[Kunal]

Would that work out to an even int or just an int?

[divya]

I think in the GMAT Prep test, the question asks whether it is an integer.

Exact question uploaded.

[divya]

exact GMATPrep question attached.

[divya]

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.

[RonPurewal]

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.