The mystery is this: first, take any three digit number,
where the first and last digits differ by two or more and
reverse the number to produce a new one.
Then subtract the smaller from the larger producing another new number.
If you reverse this number and this time add the two,  
answer is always 1089 - Math is Fun.

C > B > A Called number A B C (reverse) ----------- (subtract) Z   Y   X   X   Y   Z (reverse) ----------- (add up) 1   0   8   9 (answer)         3 > 2 > 1 1 2 3 (reverse) ----------- (subtract) 1   9   8   8   9   1 (reverse) ----------- (add up) 1   0   8   9 (answer)                                                                         9 > 7 > 5 5 7 9 (reverse)  ---------- (subtract) 3   9   6   6   9   3 (reverse) ----------- (add up) 1   0   8   9 (answer)         8 > 3 > 2 2 3 8 (reverse) ----------- (subtract) 5   9   4   4   9   5 (reverse) ----------- (add up) (answer)