A Puzzle For Dave: This is from Sunday's Parade magazine, a newspaper insert. (I wrote it from memory). A mathematics professor always wanted his daughter to do well in school. Through the years he spent lots of time coaching his daughter through difficult math problems and she became quite good at it. Soon, she left for college to study mathematics (of course). One day, during a break, she brought home a problem that even he could not figure out: What three letters come next in this equation? The answer...