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 $$9$$. 
When from any three-digit number we subtract that number written backwards, the difference will always be a number that is divisible by:． 
  * $$7$$ 
  * $$2$$ 
  * $$5$$ 
  * $$9$$ 