By Cindy Neuschwander, Author & Wayne Geehan, Illustrator. For fans of the Sir Cumference series with Pi on their mind, here is the second installment in this fun look at math and language. This time the math adventure is centered around a potion that changes 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. Perfect for parent and teachers who are looking to make math fun and accessible for everyone. For ages 6 and up.