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

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Joined: 10 May 2004
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Is the odd integer X a prime number? 1) X+2 is a prime [#permalink]

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02 Jul 2004, 09:51
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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

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02 Jul 2004, 10:28
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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Paul

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02 Jul 2004, 13:03
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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02 Jul 2004, 13:09
hi ...

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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02 Jul 2004, 13:20
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.

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Paul

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02 Jul 2004, 16:00
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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ash
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02 Jul 2004, 16:00
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# Is the odd integer X a prime number? 1) X+2 is a prime

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