3 and 17
All prime numbers greater than 2 are odd numbers. For an odd prime to be written as the sum of two primes, one of the primes must be 2 because two odd primes will produce an even sum. 11 cannot be written as the sum of two primes. 13 = 2 + 11. 17 cannot be written as the sum of two primes. 19 = 2 + 17.
3 + 17 = 20
They are: 2+7+11 = 20
Not always as for example 20+9 = 29 which is a prime number
17 and 3 are two prime numbers whose sum is 20. Their product is 51.
3 and 17
(2,3) and (2,5) are the two pairs such that the sum of their elements is a prime number.
-20
13 + 7 1 + 193 + 17
The largest prime less than 20 is 19. The largest prime over 60 is 61. The sum of these two numbers is 80.
2 + 3 = 5
All prime numbers greater than 2 are odd numbers. For an odd prime to be written as the sum of two primes, one of the primes must be 2 because two odd primes will produce an even sum. 11 cannot be written as the sum of two primes. 13 = 2 + 11. 17 cannot be written as the sum of two primes. 19 = 2 + 17.
148
It is 75.
3 + 17 = 20
They are: 2+7+11 = 20