This column discusses five children's books selected to develop math concepts involving problem solving, reasoning, and communication. The books are "Only One" (Marc Harshman); "The Librarian Who Measured the Earth" (Kathryn Lasky); "Counting Jennie" (Helena C. Pittman); "The Search for Delicious" (Natalie Babbitt); and "The Toothpaste Millionaire" (Jean Merrill). (JB)