India, Aug. 31 -- In the very first edition of Problematics, which I published in a local newspaper in my hometown in 1993, the inaugural puzzle involved three variables and two equations to work with. Now everyone knows, of course, that fewer equations than variables cannot determine a unique set of values. But as puzzlers, we also know that we can work with those equations to derive more equations. That was the basis of my first puzzle-and it is also the basis of my latest one below.

#Puzzle 210.1

A bookstore has 89 copies of Oliver Twist, 28 copies of Great Expectations, and 41 copies of David Copperfield. They are all paperbacks from the same publisher. This means that each copy of any given book has the same number of pages. The st...