A community for students.
Here's the question you clicked on:
 0 viewing
anonymous
 one year ago
The sum of the first 1 million primes is N. Without knowing N's value, one can determine that the ones'digit of N cannot be
A) 1
B) 2
C) 3
D) 9
anonymous
 one year ago
The sum of the first 1 million primes is N. Without knowing N's value, one can determine that the ones'digit of N cannot be A) 1 B) 2 C) 3 D) 9

This Question is Closed

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Let's think about this. The set of prime numbers, beginning with 2 is: {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, ...} Do you notice anything strange? Only one of those numbers is even, and that's because if any number in that list other than 2 were even, it'd be divisible by 2, and not be a prime number. So, that means that every prime number except for the first one is an odd number. When you add 2 odd numbers, you get an even number. If you add an even number and an odd number, you get an odd number. So, in the first 1000000 primes, you're adding 1 even number and 999999 odd numbers. So, based on that, can you get your answer?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Yeah, it'd be B or rather, it cannot be any even number in the units digit. THis is because adding 999999 odd numbers will still yield an odd number since you're adding an odd number of odd numbers. So, finally, you're adding 2 with that odd number, making the units digit of N an odd number.

EntwinedFates
 one year ago
Best ResponseYou've already chosen the best response.0Understood, thanks! :)

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Ohh i see now thanks!
Ask your own question
Sign UpFind more explanations on OpenStudy
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.