please help GmapPrep question

[drgmatIL]

I found that N = 15,y=2
1. 1/30
2.1/45
3.1/75

none of them is integer...

where I'm wrong?

[*arch*]

Hey.. I made the same mistake as well and chose "None" in the test.

But i guess you can also look at it this way:-

450 y = n^3; (3*3*5*5*2)*y = n^3; Therefore y = (n^3) / (3*3*5*5*2)

Option I --> y / (3*2*2*5) --> n^3 / (3*3*3*2*2*2*5*5*5)

Note the denominator of n^3 now has integers 3, 2 and 5 all with powers of 3. That makes n^3 an integer.

Try this with Options 2 and 3 - but you won't end up with cubes in the denominator. That's why the Answer is (I).

Plz correct me if i'm wrong!

[pepeprepa]

arch I think the thing you should add to your reasoning is that n has at least 2.3.5 among its factors.
Because with 1) we arrive at (n/2*3*5)^3
This is not an integer if n=10 for example. n at least has 2*3*5 among its factors and we know that thanks to y*450=n^3

[siddarth]

the answer should be E (all the options will yield) integers

[Ian Stewart]

The answer is B, not E.

I found that N = 15,y=2
where I'm wrong?

You must have multiplied incorrectly; 15^3, an odd number, cannot be equal to 450*2 = 900, which is even.

I posted a solution to this problem here:

www.beatthegmat.com/number-properties-q-t13973.html

[siddarth]

The answer is B, not E.

I found that N = 15,y=2
where I'm wrong?

You must have multiplied incorrectly; 15^3, an odd number, cannot be equal to 450*2 = 900, which is even.

I posted a solution to this problem here:

www.beatthegmat.com/number-properties-q-t13973.html

The answer is B Indeed, i was wrong, did not pay too much attention....thanks