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#### Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here. # GRE math Challenge #43-If N = 3^x*5^y, where x and y  Question banks Downloads My Bookmarks Reviews Important topics
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Director  Joined: 16 May 2014
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GRE math Challenge #43-If N = 3^x*5^y, where x and y [#permalink]
Expert's post 00:00

Question Stats: 100% (01:06) correct 0% (00:00) wrong based on 8 sessions
If $$N = 3^x*5^y$$, where x and y are positive integers, and N has 12 positive factors, what is the value of N?

 Column A Column B 9 is not a factor 125 is a factor

A. Only Column A is sufficient.
B. Only Column B is sufficient.
C. Column A and B both are needed
D. Column A and B both are insufficient
E. None of the columns are needed.
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If you find this post helpful, please press the kudos button to let me know ! Intern Joined: 26 Mar 2015
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Re: GRE math Challenge #43 [#permalink]
That is not a GRE question, just FYI.

Posted from my mobile device Director  Joined: 16 May 2014
Posts: 595
GRE 1: Q165 V161 Followers: 94

Kudos [?]: 456 , given: 64

Re: GRE math Challenge #43 [#permalink]
Expert's post
Yes you are right!
The idea is to solve maths problems regardless what exam it is. Just to challenge brains. _________________

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If you find this post helpful, please press the kudos button to let me know ! Manager Joined: 27 Sep 2017
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Re: GRE math Challenge #43-If N = 3^x*5^y, where x and y [#permalink]
soumya1989 wrote:
If $$N = 3^x*5^y$$, where x and y are positive integers, and N has 12 positive factors, what is the value of N?

 Column A Column B 9 is not a factor 125 is a factor

A. Only Column A is sufficient.
B. Only Column B is sufficient.
C. Column A and B both are needed
D. Column A and B both are insufficient
E. None of the columns are needed.

For me, the ans would be A, we are told that $$N = 3^x*5^y$$, where x and y are positive integers, and N has 12 positive factors.

then (x+1)(y+1)=12. Let us do some prime factorization of 12.

12=2*6=1*12=3*4 We should rule out the pair 1*12 since x+1 or y+1=1, then x or y=0. Yet, we are told that x and y are positive integers. Now for cloumn A, we are told that 9 is not a factor of N. This leads us to know x=1 and y=5. then $$N = 3^1*5^5$$.

For column B, we are told that 125 is a factor. That means that y>=3. So, y would be 3 or 5. B can't help us decide the value of N.

ANS:A Re: GRE math Challenge #43-If N = 3^x*5^y, where x and y   [#permalink] 11 Mar 2018, 05:38
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# GRE math Challenge #43-If N = 3^x*5^y, where x and y  Question banks Downloads My Bookmarks Reviews Important topics Powered by phpBB © phpBB Group Kindly note that the GRE® test is a registered trademark of the Educational Testing Service®, and this site has neither been reviewed nor endorsed by ETS®.