Two digit number "AB" = 10A + B
Add together the digits = A + B
Subtract from original: (10A + B) - (A + B) = 9A
This number is a multiple of 9.
The symbols for (1x9), (2x9), (3x9), (4x9), (5x9), (6x9), (7x9), (8x9), and (9x9) are the same, see image below. They are guaranteed to be...