Magical Mind Reader

Select any number between 10 and 99 in your mind. Add the two digits of number and subtract the result from the original number. Now see the sign for final number from the table above. Concentrate on the red circle for an instance and click it ,you will see the sign for the resulting number
For eg. select 76. add 7+6=13, subtracty 13 from 76=63.

Try to Guess the logic behind this game.If you get post it as Comment.