There are 2 two digit numbers such that one has been obtained by swapping the digits of the other.
On subtracting the smaller number from the larger number, I get a number divisible by :
Let the number be ab.
(10a + b) – (10b + a) = 10a + b – 10b – a
= 9a – 9b = 9(a – b).
Hence, the number is divisible by 9 and also divisible by 3.