I started out trying to subtract a prime number from 85, and then
see whether I had a prime number remaining. I did this several
times, before I slapped myself upside the head.
-- 85 is an odd number.
-- To get an odd-number for a sum, you have to add one odd number
to one even number ... there's no other way.
-- So one of the prime numbers we're looking for must be
an even number.
-- The ONLY even number that's a prime number is ' 2 '.
So it must be one of them.
-- Subtract 2 from 85, and you have 83 left.
Is 83 a prime number ? Yes.
-- So the two numbers are 2 and 83.
If 83 were not a prime number, this wouldn't work, and I would have said
"There is no such pair of numbers.". That means it doesn't necessarily work
for every odd number.
Examples:
75 ===> 2 and 73 . \
55 ===> 2 and 53 . \
45 ===> 2 and 43 . \
Both primes. It works.
65 ===> 2 and 63 . 63 is not a prime. \
35 ===> 2 and 33 . 33 in not a prime. \
It doesn't work.