PUZZLE #48 Responses/hints

If you tried this mystery puzzle with an actual number or two you noticed that there were several things which always happened.

First, if the number was like 212, then the difference is 0, so assume the number does not start and end with the same digit.

Then the middle number is always 9, and the difference between 9 and the first number is always the last number.

In fact it is not too hard to explain, all you need to think about is how subtraction is defined?

Example: Choose the number 123, then we have 321 as the reverse number, and by subtraction we get:

321

-123

198

where 9 – 1 = 8.