Sir Cumference Pack (Sir Cumference and the Dragon of Pi; Sir Cumference and the First Round Table; Sir Cumference and the Sword in the Cone) by Cindy Neuschwander (2002-08-01)

Sir Cumference, Lady Di Ameter, and their son Radius appear in three fun math adventures. In the first book, The Circumscribers might be preparing to make war on the kingdom of Sir Arthur. In this clever tale, the author weaves a description of basic mathematical shapes into an interesting plot that teaches important circle terms and concepts, such as: radius, diameter, area circuference and more. In the second book, a potion has changed Sir Cumference into a fire breathing dragon. Can Radius change him back? Join Radius on his quest through the castle to solve a riddle that will reveal the cure. It lies in discovering the magic number that is the same for all circles. Book three has Sir Cumference helping Sir Vertex seek the sword in the cone. King Arthur has hidden his sword, Edgecaliber. The knight who finds it will be the next king.