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Is the odd integer X a prime number? 1) X+2 is a prime

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Is the odd integer X a prime number? 1) X+2 is a prime [#permalink] New post 02 Jul 2004, 08:51
Is the odd integer X a prime number?
1) X+2 is a prime number.
2) X-3 is a prime number.

A B C D E

Please explain yours answer
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 [#permalink] New post 02 Jul 2004, 09:28
C it is. 1 min
1) 5 and 7 are primes but 9 and 11 --> 9 is not prime
2) 5 and 2 are primes but 8 and 5 --> 8 is not prime
both combined, the only primes with a differential of 5 is 2-5-7.
X = 5 --> prime
x+2 = 7 --> prime
x-3 = 2 --> prime
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 [#permalink] New post 02 Jul 2004, 12:03
I've got B.
It says that x is odd, so from B) odd - odd =even=prime, even prime is only 2
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 [#permalink] New post 02 Jul 2004, 12:09
hi ...

the answer is B ....
when the Q sayz odd ... we know that only 5 - 3 =2 which is a prime ... and so the number X is nothing but the number 5...
other all prime nos are odd certainly... but odd- odd will give only even and any even noz is never a prime...and that is why only 5 is the noz..

A is no enough...

Hope that helps!

Have fun :)
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 [#permalink] New post 02 Jul 2004, 12:20
You are right guys. question says "odd integer X" so X has to be odd. I overlooked that when I gave the 2nd stem example. 8-3.
8 cannot be for it has to be odd.
:stupid2
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 [#permalink] New post 02 Jul 2004, 15:00
A is not sufficient as above.

B is sufficient. Here is how I solved it.

any odd number = 2K+1

2K+1 - 3 = 2(K-1) which is always even.

- ash
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  [#permalink] 02 Jul 2004, 15:00
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Is the odd integer X a prime number? 1) X+2 is a prime

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