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A “Sophie Germain”

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by sanju09 » Tue Jul 27, 2010 12:54 am
A “Sophie Germain” prime is any positive prime number p for which 2p + 1 is also prime. The product of all the possible units digits of Sophie Germain primes greater than 5 is:
a. 3
b. 7
c. 21
d. 27
e. 189

[spoiler]Source: Manhattan GMAT Challenge Problem of the Week – 8 June 2010[/spoiler]
The mind is everything. What you think you become. –Lord Buddha



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by gmatmachoman » Tue Jul 27, 2010 1:07 am
sanju09 wrote:A “Sophie Germain” prime is any positive prime number p for which 2p + 1 is also prime. The product of all the possible units digits of Sophie Germain primes greater than 5 is:
a. 3
b. 7
c. 21
d. 27
e. 189

[spoiler]Source: Manhattan GMAT Challenge Problem of the Week – 8 June 2010[/spoiler]
p =11,17,23,29

Product of Unit digits 1*7*3*9 = 189

Pick E
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by shankysainik » Tue Jul 27, 2010 1:23 am
I think it would be 1*3*9 as 17 is not a Sophie's prime.
Hence, 27 is the answer.
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by sanju09 » Tue Jul 27, 2010 1:44 am
shankysainik wrote:I think it would be 1*3*9 as 17 is not a Sophie's prime.
Hence, 27 is the answer.

This tells us more about it…

https://primes.utm.edu/top20/page.php?id=2

I wish a bigwig abridge this high-quality but stretched explanation…

https://www.beatthegmat.com/mba/2010/06/ ... -june-2010
The mind is everything. What you think you become. –Lord Buddha



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