If 'ABC', a 3 digit number is reversed then the sum of digits of the difference between the original and the reversed number will always be divisible by:
All of these
ABC can be written as 100A + 10B + C
Similarly CBA can be written as 100C + 10B + A
ABC - CBA = (100A + 10B + C) - (100C + 10B + A)
= 100A + 10B + C - 100C - 10B - A
= 99 (A - C)
=9×11(A−C)=3×3×11(A−C)
This number is divisible by 3,9,11 and 99.
If a number is divisible by 9 and 3, the sum of the digits of that number must be divisible by 9 and 3 respectively.