A Harry Potter math trick from the WSJ

[pippin_999]

This from Sharon Begley's column in today's  Wall Street 
Journal:

Prove to your kids that you've memorized the first world of every 
page in the current Harry Potter:
   Ask them to pick any three digit number except a triplet like 444.
Then reverse the digits. Subtract the smaller from the larger. Tell 
them the first word of that page (you do have to memorize the 
first word of a few pages.) 

It works because the difference between any two three-digit 
numbers XYZ and ZYX is a multiple of ninety-nine. 

Pippin
whose house also waves to Tabouli's