28
if you mean what three prime numbers add up to a prime number then the answer is : 5 + 7 + 11 = 23
21
5+13
Same as average. For example, if you have 5 numbers, add them all up, then divide the result by 5. If you have 10 numbers, you add and divide by 10, etc.
37
0
35
15
5
5 and -4
28
false none of the numbers add up to 31
if you mean what three prime numbers add up to a prime number then the answer is : 5 + 7 + 11 = 23
21
31 and 5
5 and 23