The prime numbers 3 an 7 are both odd and sum to 10.
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They add up to 17
The sum of the five odd numbers between 10 and 20 is: sum = 5 x (11 + 19) / 2 = 75.
For a 2-digit prime number (which are all odd) to be the sum of two prime numbers, one of the prime numbers will have to be 2. That means the difference between the sum and the other addend will have to be 2. Prime numbers that differ by 2 are called twin primes. There are six pairs of 2-digit twin primes. Your numbers are 13, 19, 31, 43, 61 and 73.
There are two sets of 3 consecutive numbers whose sum is 30 but neither set contains all odd numbers. The two sets are: 8, 10 and 12 as well as 9, 10 and 11.
Sure. All composite numbers can be written as a product of primes. It shouldn't be tough to find a composite number that's the sum of three other composite numbers. Let's try 30. 2 x 3 x 5 = 30 Product of primes, check. 6 (2 x 3) + 10 (2 x 5) + 14 (2 x 7) = 30 Sum of three products of primes, check.