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# Is N an integer? 1) 2N is an integer 2) 5N is an integer (DS)

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Intern
Joined: 06 Mar 2016
Posts: 15
Is N an integer? 1) 2N is an integer 2) 5N is an integer (DS)  [#permalink]

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09 Sep 2018, 09:19
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35% (medium)

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71% (01:02) correct 29% (01:05) wrong based on 17 sessions

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Is N an integer? 1) 2N is an integer 2) 5N is an integer

I read a related post at following link - https://gmatclub.com/forum/is-n-an-inte ... 61417.html
But somehow i could not figure out how they have concluded C as an answer option.

Director
Joined: 20 Feb 2015
Posts: 727
Concentration: Strategy, General Management
Re: Is N an integer? 1) 2N is an integer 2) 5N is an integer (DS)  [#permalink]

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09 Sep 2018, 10:11
divyajoshi12 wrote:
Is N an integer? 1) 2N is an integer 2) 5N is an integer

I read a related post at following link - https://gmatclub.com/forum/is-n-an-inte ... 61417.html
But somehow i could not figure out how they have concluded C as an answer option.

1) 2N is an integer
this is possible when N = 1/2 , 3/2,5/2(basically divided by 2) ,0 , any other +ve of -ve integers
insufficient

2) 5N is an integer
same as above
N = 1/5 , 2/5,3/5,4/5(basically divided by 5) , 0 , any other +ve of -ve integers
insufficient

using both

we can have N = either 0 or any other +ve of -ve integers
in both the cases N should be an integer
sufficient
C
GMAT Tutor
Status: GMATH founder
Joined: 12 Oct 2010
Posts: 167
Re: Is N an integer? 1) 2N is an integer 2) 5N is an integer (DS)  [#permalink]

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09 Sep 2018, 11:36
divyajoshi12 wrote:
Is N an integer?
1) 2N is an integer
2) 5N is an integer

$$N\,\mathop = \limits^? \,\,\operatorname{int}$$

$$\left( 1 \right)\,\,2N = \operatorname{int} \,\,\,\,\left\{ \begin{gathered} \,N = 0\,\,\,\, \Rightarrow \,\,\,\,\left\langle {{\text{YES}}} \right\rangle \hfill \\ \,N = \frac{1}{2}\,\,\,\, \Rightarrow \,\,\,\,\left\langle {{\text{NO}}} \right\rangle \hfill \\ \end{gathered} \right.$$

$$\left( 2 \right)\,\,5N = \operatorname{int} \,\,\,\,\left\{ \begin{gathered} \,N = 0\,\,\,\, \Rightarrow \,\,\,\,\left\langle {{\text{YES}}} \right\rangle \hfill \\ \,N = \frac{1}{5}\,\,\,\, \Rightarrow \,\,\,\,\left\langle {{\text{NO}}} \right\rangle \hfill \\ \end{gathered} \right.$$

$$\left( {1 + 2} \right)\,\,\,N = 5N - 2\left( {2N} \right)\,\,\,\mathop = \limits^{\left( 1 \right)\,\,{\text{and}}\,\,\,\left( 2 \right)} \,\,\,\operatorname{int} - 2 \cdot \operatorname{int} = \operatorname{int} - \operatorname{int} = \operatorname{int} \,\,\,\,\, \Rightarrow \,\,\,\,{\text{SUFF}}.$$

This solution follows the notations and rationale taught in the GMATH method.

Regards,
fskilnik.
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Fabio Skilnik :: http://www.GMATH.net (Math for the GMAT)
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Re: Is N an integer? 1) 2N is an integer 2) 5N is an integer (DS) &nbs [#permalink] 09 Sep 2018, 11:36
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