It is currently 22 Feb 2018, 14:44

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# If N is a positive odd integer, is N prime?

Author Message
TAGS:

### Hide Tags

Board of Directors
Joined: 01 Sep 2010
Posts: 3482
If N is a positive odd integer, is N prime? [#permalink]

### Show Tags

27 Jul 2017, 07:02
Top Contributor
7
This post was
BOOKMARKED
00:00

Difficulty:

75% (hard)

Question Stats:

51% (01:29) correct 49% (01:26) wrong based on 220 sessions

### HideShow timer Statistics

If N is a positive odd integer, is N prime?

(1) $$N = 2^k+ 1$$ for some positive integer k.

(2) N + 2 and N + 4 are both prime.
[Reveal] Spoiler: OA

_________________
Math Expert
Joined: 02 Aug 2009
Posts: 5660
If N is a positive odd integer, is N prime? [#permalink]

### Show Tags

27 Jul 2017, 08:00
1
KUDOS
Expert's post
1
This post was
BOOKMARKED
carcass wrote:
If N is a positive odd integer, is N prime?

(1) $$N = 2^k+ 1$$ for some positive integer k.

(2) N + 2 and N + 4 are both prime.

hi...

lets see the statements..

(1) $$N = 2^k+ 1$$ for some positive integer k.
if k = 2, N = $$2^2+1=5$$.. YES
if k= 3, N=$$2^3+1=9$$... No
Insuff

(2) N + 2 and N + 4 are both prime
if N+2 and N+4 are prime, ONE of N or N+2 or N+4 will surely be MULTIPLE of 3..
so N can be prime only when N=3, otherwise always NO
Insuff

combined
Nothing new

E
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

BANGALORE/-

Manager
Joined: 22 Sep 2016
Posts: 211
Location: India
GMAT 1: 710 Q50 V35
GPA: 4
Re: If N is a positive odd integer, is N prime? [#permalink]

### Show Tags

27 Jul 2017, 08:08
1
KUDOS
carcass wrote:
If N is a positive odd integer, is N prime?

(1) $$N = 2^k+ 1$$ for some positive integer k.

(2) N + 2 and N + 4 are both prime.

from 1, k=1,2 satisfy, but k=3 doesn't.
insuff

from 2, N=1, 3 satisfy, but 1 is neither prime nor composite.
insuff

together, N =3 satisfies both the criteria.
_________________

Desperately need 'KUDOS' !!

Director
Joined: 21 May 2013
Posts: 581
If N is a positive odd integer, is N prime? [#permalink]

### Show Tags

27 Jul 2017, 08:12
rekhabishop wrote:
carcass wrote:
If N is a positive odd integer, is N prime?

(1) $$N = 2^k+ 1$$ for some positive integer k.

(2) N + 2 and N + 4 are both prime.

from 1, k=1,2 satisfy, but k=3 doesn't.
insuff

from 2, N=1, 3 satisfy, but 1 is neither prime nor composite.
insuff

together, N =3 satisfies both the criteria.

Answer will be E , N can be 3 or 9.
Intern
Joined: 22 Mar 2017
Posts: 28
GMAT 1: 680 Q48 V35
If N is a positive odd integer, is N prime? [#permalink]

### Show Tags

08 Jan 2018, 06:18
If N is a positive odd integer, is N prime?

(1) N=2^k+1N for some positive integer k.

N can be 3, 5, or 9 using values of k = 1, 2 and 3 respectively

INSUFF

(2) N + 2 and N + 4 are both prime.

If N = 3 then N + 2 = 5 and N + 4 = 7 COMPLIES (we pick the first prime of the examples used for S1).
If N = 9 then N + 2 = 11 and N + 4 = 13 COMPLIES (we pick the first non-prime of the examples used for S1).

INSUFF

(1)(2)

Same examples fulfill both Ss (in this case the prime 3 and the non-prime 9).

INSUFF

AC: E

-
_________________

If it helped, some kudos would be more than welcome!

King regards,

Rooigle

If N is a positive odd integer, is N prime?   [#permalink] 08 Jan 2018, 06:18
Display posts from previous: Sort by