CLASS IX CLASSIX – PART V

Why?

Ohm: There is no 3!
Om: III?
Ohm: Something like that...
Om: Why 9?
Ohm: IX?
Om: Exactly, that!
Ohm: For any 'n' digit number expressed x(1)x(2)x(3)....x(n), x(i) being the i-th digit, the number is the largest 'n' digit number if and only if x(i) = 9 for all i from 1 to n, if I were to unnecessarily complicate the simplest of things, for plain simple harmless fun!
Om: Oh! There you go! So there is no part III?
Ohm: There is, hidden!
Om: Ah! So I see!
Ohm: But why 9 again?
Om: Only the presence of IX alters not the digital sum of any number!
Ohm: Basis?
Om: The base is 10 my friend, only 10!
Ohm: Zero?
Om: Oh yeah, that too - But a zero is no fun, if you ask me!
Ohm: Oh! Yummy!
Om: And this, is part 5!