100 can be expressed as the sum of two primes in 6 different ways (ignoring order):
100 = 3+97 = 11+89 = 17+83 = 29+71 = 41+59 = 47+53
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100 = 62 + 82 = 82 + 62 and there is no other way
12=5+7
Each one of them can be expressed as a sum of two primes.
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.
1 + 17 = 18 5 + 13 = 18 7 + 11 = 18
The sum of two odd primes is always an even answer or number.
It is: 19+79 = 98
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It is: 2+13 = 15
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It is not. Of the infinitely many primes only one (the number 2) is even, the rest are all odd. The sum of any two primes other than 2 is even and therefore not a prime. If one of the primes in the sum is 2 then the sum is a prime only if the other is the lower of a pair of twin primes. So, while it is possible, it is certainly more likely that the sum is a composite.
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