Let's take a two digit number 'ab'. Its general form is 10 × a + 1 × b. When we reverse the digits, the new number will be of the form 10 × b + 1 × a.
If we add both the numbers we get
(10 × a + 1 × b) + (10 × b + 1 × a)
=10a + b + 10b + a
= 11(a+b)
Hence, when divided by 11 it will not leave any remainder.