No matter how we write the three-digit number, the sum of its three digits is always the same. Therefore, the remainders of the two numbers divided by $$9$$ are also the same. The difference will always be a number that is divisible by $$9$$. 
(US $$1998$$ Math kangaroo Problems, Level $$5-6$$, Question \#$$15$$)When from any three-digit number we subtract that number written backwards, the difference will always be a number that is divisible by:． 

A) $$7$$ 
B) $$2$$ 
C) $$5$$ 
D) $$9$$ 
E) $$13$$ 