GRE Prep Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
GRE Prep Club Team Member
Joined: 20 Feb 2017
Posts: 2506
Given Kudos: 1053
GPA: 3.39
A “Sophie Germain” prime is any positive prime number p for which 2p +
[#permalink]
21 Apr 2021, 15:58
21 Apr 2021, 15:58
12
Expert Reply
33
Bookmarks
00:00
Question Stats:
30% (03:06) correct
69% (02:36) wrong based on 208 sessions
Hide Show timer Statistics
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
A. 3
B. 7
C. 21
D. 27
E. 189
Re: A “Sophie Germain” prime is any positive prime number p for which 2p +
[#permalink]
05 Jul 2021, 04:42
05 Jul 2021, 04:42
18
2
Bookmarks
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.
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.
General Discussion
Re: A Sophie Germain prime is any positive prime number p for which 2p +
[#permalink]
15 May 2022, 16:02
15 May 2022, 16:02
can this question type appear on the exam?
