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Re: A Sophie Germain prime is any positive prime number p for which 2p + [#permalink]
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Etamo wrote:
can this question type appear on the exam?


Yes. it is just a wording question about primes. However, in the first part of the stem clearly, the question gives you the direction and meaning.

yes could be. I do not see it is out of scope
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Re: A Sophie Germain prime is any positive prime number p for which 2p + [#permalink]
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I would add, though, as this is a NON official question. And you see this from the piece of information " any positive prime "

Prime numbers are ONLY positive, does not exist a negative prime number

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Re: A Sophie Germain prime is any positive prime number p for which 2p + [#permalink]
Okay. Thank you
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Re: A Sophie Germain prime is any positive prime number p for which 2p + [#permalink]
mrk9414 wrote:
A prime number greater than 5 can have only the following four units digits: 1, 3, 7, or 9.

If the units digit of p is 1 then the units digit of 2p+1 would be 3, which is a possible units digit for a prime. For example consider p=11=prime --> 2p+1=23=prime;

If the units digit of p is 3 then the units digit of 2p+1 would be 7, which is a possible units digit for a prime. For example consider p=23=prime --> 2p+1=47=prime;

If the units digit of p is 7 then the units digit of 2p+1 would be 5, which is NOT a possible units digit for a prime;

If the units digit of p is 9 then the units digit of 2p+1 would be 9, which is a possible units digit for a prime. For example consider p=29=prime --> 2p+1=59=prime.

The product of all the possible units digits of Sophie Germain primes greater than 5 is 1*3*9=27.

Answer: D.


What about 41?? 41*2+1 = 83 (prime) & 53*2+1=107(prime)

It would go on for infinite.
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