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If n and y are positive integers and 450y=n^3

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Re: If n and y are positive integers and 450y=n^3  [#permalink]

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New post 29 Dec 2016, 11:10
abhi758 wrote:
If x and y are positive integers and 450y=x^3, which of the following must be an integer?

i) \(\frac{y}{{3*2^2*5}}\)
ii) \(\frac{y}{{3^2*2*5}}\)
iii) \(\frac{y}{{3*2*5^2}}\)

a. None
b. i only
c. ii only
d. iii only
e. i, ii and iii

Please explain your answers..



\(450y=x^3\)

\(5^2*2*3^2*y = x^3\)

The minimum value of \(y =\) \(2^2*5*3\)

Hence, among the given options, only (I) is possible...

So, correct answer must be (B)

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Re: If n and y are positive integers and 450y=n^3  [#permalink]

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New post 22 Jan 2017, 06:58
1)If cube root of 450y is an integer, then 450y has to have three of each prime factors. 2)Prime factors of 450 are 2*5*5*3*3. It is missing two 2's, one 5, and one 3. 3)To compensate for these missing factors y has to have all of them as its prime factors, consequently y has to be divisible by 2^2*5*3.
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Re: If n and y are positive integers and 450y=n^3  [#permalink]

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New post 26 Jan 2017, 15:24
1) x is cubed, which means that its prime factors can be divided into three identical sets.
2) 450*y should have the same three sets of prime factors as x cubed, since the two expressions are equal
3) The prime factors of 450 are 2*5*5*3*3. This means that y has to consist of 2^2*5*3 at least, and it has to be divisible by this expression.

The correct answer is B.
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Re: If n and y are positive integers and 450y=n^3  [#permalink]

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New post 29 Jun 2017, 23:04
Cant we take higher values of N and Y so that it satisfies the equation,the all 3 possiblities are correct and answer is E
eg:
y= 5^4*3^4*2^5
N=5^2*3^2*2^2
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Re: If n and y are positive integers and 450y=n^3  [#permalink]

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New post 29 Jun 2017, 23:18
jakexix wrote:
Cant we take higher values of N and Y so that it satisfies the equation,the all 3 possiblities are correct and answer is E
eg:
y= 5^4*3^4*2^5
N=5^2*3^2*2^2


The question asks which of the following MUST be an integer, not COULD be an integer. If y = 2^2*3*5, which is the least possible value of y, then only B is true. Please re-read the thread and follow the links to similar questions to understand the concept better.
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Re: If n and y are positive integers and 450y=n^3  [#permalink]

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New post 03 Dec 2018, 05:19
Bunuel wrote:
jakexix wrote:
Cant we take higher values of N and Y so that it satisfies the equation,the all 3 possiblities are correct and answer is E
eg:
y= 5^4*3^4*2^5
N=5^2*3^2*2^2


The question asks which of the following MUST be an integer, not COULD be an integer. If y = 2^2*3*5, which is the least possible value of y, then only B is true. Please re-read the thread and follow the links to similar questions to understand the concept better.



Hey Bunuel,

I have a query. Why are we considering only minimum value of y?

y = 2^8 * 3^7 * 5^7 also gives a integer value for n.
In that case, all the 3 options gives integers.

Please clarify. What am I missing here?
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Re: If n and y are positive integers and 450y=n^3 &nbs [#permalink] 03 Dec 2018, 05:19

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