Question

If a number A is a 2 digit number and its digits are transposed to form number B, then the difference between the larger of the two numbers and the smaller of the two numbers must be divisible by:

Answer 1

if A=ab and B=ba then A-B=ab-ba which means 10a+b-10b-a=9a-9b=9(a-b)
so A-B is divisible by 9