While answering questions on Brainly, I ran into a lot of them
that talked about a set being 'closed'. I didn't know what that
means, so do ya know what I did ? I went and looked it up.
I found it, and then I read about it, and now I know what it means !
A set that's 'closed under addition' means that if you add two numbers
in the set, you get another number that's also in the set.
Let's see:
-- 3 is a prime number
-- 5 is a prime number
-- (3+5) = 8
-- 8 is NOT a prime number
-- We added two prime numbers and got a number that is NOT prime.
So the set of prime numbers is NOT closed under addition.
