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Is the postive integer n an odd number (1) n + 4 is a prime

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Is the postive integer n an odd number (1) n + 4 is a prime [#permalink] New post 23 Jul 2011, 21:07
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A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

87% (02:11) correct 13% (00:17) wrong based on 15 sessions
Is the postive integer n an odd number

(1) n + 4 is a prime number

(2) n + 3 is not a prime number
[Reveal] Spoiler: OA
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Re: prime number? [#permalink] New post 23 Jul 2011, 21:16
siddhans wrote:
Is the postive integer n an odd number

(1) n + 4 is a prime number

(2) n + 3 is not a prime number



It seems 'A' is the correct one.

taking (1),

n + 4 is a prime number
==> n must be an odd number (there is no even number, except 2, is also the prime number)

taking (2)
n + 3 is not a prime number ==> n can be even number (ex. 16) or an odd number (ex. 14)

So (1) alone is suffiicient to answer the question, while (2) alone is not
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Re: prime number? [#permalink] New post 23 Jul 2011, 21:19
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siddhans wrote:
Is the postive integer n an odd number

(1) n + 4 is a prime number

(2) n + 3 is not a prime number


n>0

1)
n+4=prime
All prime but 2 are odd and n+4 can't be 2.
odd+even=odd
Thus, n=odd
Sufficient.

2)
n+3 Not prime
n=6; n+3=9. Not prime. n=even
n=7; n+3=10. Not prime. n=odd
Not Sufficient.

Ans: "A"
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Re: prime number?   [#permalink] 23 Jul 2011, 21:19
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