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Is 3n an integer? (1) 6n is an integer. (2) 9n is an integer.

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Is 3n an integer? (1) 6n is an integer. (2) 9n is an integer.  [#permalink]

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New post 15 Apr 2016, 01:31
1
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A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

43% (01:22) correct 57% (01:06) wrong based on 60 sessions

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Is 3n an integer? (1) 6n is an integer. (2) 9n is an integer.  [#permalink]

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New post 15 Apr 2016, 02:10
St1: 6n is integer --> n can be 1/2, 1/3, 1/6,.......
If n = 1/3 then 3n is an integer
If n = 1/2 then 3n is not an integer
Not Sufficient

St2: 9n is an integer --> n can be 1/3, 1/9, .....
If n = 1/3 then 3n is an integer
If n = 1/9 then 3n is not an integer
Not Sufficient

Combining St1 and St2: n can be 1/3, 2/3, 6/9 or any integer
3n will always be integer.
Sufficient

Answer: C
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Is 3n an integer? (1) 6n is an integer. (2) 9n is an integer.  [#permalink]

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New post 26 Aug 2018, 18:17
1
pikolo2510 niks18 chetan2u gmatbusters VeritasKarishma Bunuel pushpitkc GMATPrepNow

Any alternative approach than picking numbers?
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Re: Is 3n an integer? (1) 6n is an integer. (2) 9n is an integer.  [#permalink]

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New post 26 Aug 2018, 23:39
1
adkikani wrote:
pikolo2510 niks18 chetan2u gmatbusters VeritasKarishma Bunuel pushpitkc GMATPrepNow

Any alternative approach than picking numbers?


hi adkikani,

Statement 1: implies \(6n=p\), for any integer \(p => 3n=\frac{p}{2}\)

now if \(p\) is even then \(3n\) is an integer, if not then \(3n\) is not an integer. insufficient

Statement 2: implies \(9n=q\), for any integer \(q => 3n=\frac{q}{3}\).

now if \(q\) is a multiple of \(3\), then \(3n\) is an integer, if not then \(3n\) is not an integer. insufficient

Combining 1 & 2: we have \(\frac{p}{2}=\frac{q}{3} => q=\frac{3p}{2}\). Now \(q\) is an integer so \(p\) has to be an even number.

Therefore from Statement 1, we have \(3n=\frac{p}{2}=Integer\). Sufficient

Option C
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Re: Is 3n an integer? (1) 6n is an integer. (2) 9n is an integer.  [#permalink]

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New post 27 Aug 2018, 03:53
1
Bunuel wrote:
Is 3n an integer?

(1) 6n is an integer.
(2) 9n is an integer.


This is how I would approach it:

(1) 6n is an integer.
6n = Integer = 2 * 3n
3n may be 'I' (an integer) or 'I/2' (in its simplest form). (No other form is possible i.e. 3n cannot be I/3 or I/4 or I/20 ins simplest form since 6n will not be integer then)

Not necessary.

(2) 9n is an integer.
So 9n = Integer = 3 * 3n
3n may be 'I' (an integer) or 'I/3' (in its simplest form). (No other form is possible i.e. 3n cannot be I/2 or I/4 or I/20 in simplest form since 9n will not be integer then)

Not necessary.

Using both, 3n must be 'I' (common to both statements).

Answer (C)
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Re: Is 3n an integer? (1) 6n is an integer. (2) 9n is an integer. &nbs [#permalink] 27 Aug 2018, 03:53
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