A number consists of two digits. If the digits interchange places and the new number is added to the original number, then the resulting number will be divisible by:

A.    3   
B.    5
C.    9   
D.    11
Ans: D

Explanation:

Let the ten's digit be x and unit's digit be y.
Then, number = 10x + y.
Number obtained by interchanging the digits = 10y + x.
(10x + y) + (10y + x) = 11(x + y), which is divisible by 11.