You're waiter puzzle reminds me of an old baseball tale, here's a version off the net:
There is an old baseball story that was, I think, first told about Frankie Frisch when he was player-manager of the St. Louis Cardinals in the 1930s:
The Cardinals' right fielder misplayed a routine fly ball into a double, and Frisch angrily took the guy out of the game, saying, "I'm going out there myself and show you how to play the outfield." A fly ball was hit to the same place and Frisch dropped it. He came back to the dugout, they say, and shouted to the right fielder, "You've got that position screwed up so bad that no one can play it!"
The explanation you provided screwed up people's understanding so bad they'll never understand it. You have to throw away that explanation and start from scratch. The gentlemen gave the waiter $30. $25 went to the restaurant, $2 went to the waiter, and $3 went back to the gentlemen.
Or you could explain it this way: The gentlemen paid 3 times $9 for a total of $27 dollars. $25 went to the restaurant and the waiter kept $2 for his tip.
Taz, please, enough already. Few would look at your problem and claim it has a common sense solution, but we're all intrigued, so what's the answer and why?
--Percy