WILL GIVE MEDAL. HELP!
If 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 _____.

Question

WILL GIVE MEDAL. HELP!
If 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 _____.

anonymous · Answer

who knows? lets try some ...
$$64-46=18$$

anonymous · Answer

divisible by 2, 3,6,9
lets try another 
$$51-14=36$$ hmm lets try some more

anonymous · Answer

$$54-45=9$$ ok maybe nine?

anonymous · Answer

wanna do it for real?

anonymous · Answer

try 
$$10a+b-(10b+a)$$ get 
$$10a-a-10b+b=9a-9b$$