That's called Arabic numerals so I think the answer is Arabians....
There are no 3 digit numbers between 0 and 9 because 0 and 9 are 1 digit numbers.
-9
9
9
9
9+0=9?
There are 10000 such codes. Each of the numbers 0-9 can be in the first position. With each such first digit, each of the numbers 0-9 can be in the second position. With each such pair of the first two digits, each of the numbers 0-9 can be in the third position. etc.
9
The sum of these numbers is 38. There are 8 numbers. The mean is thus:38/8 = 4.75
The two square numbers that add up to 9 are 0 and 9. Specifically, (0^2 = 0) and (3^2 = 9), and their sum is (0 + 9 = 9). Another pair is (1^2 = 1) and (2^2 = 4), which also gives (1 + 4 = 5), but does not meet the requirement. Therefore, the only valid pair is 0 and 9.
0 1 8
9