There's just one little problem with the add up the digits theory.....

11 x 9 = 99

9 + 9 = 18

OR

9 - 9 = 0

- W -

* Meh *

How is that a problem? All those are divisible by nine.

Not that one, the add up the total to get 9 theory....

9 x 8 = 72 where 7 + 2 = 9

It doesn't work for 11 or 12 or any higher number for that matter.