The Mayan number system

Erika Roldan is a mathematician from Mexico, who specialises in the history and philosophy of math and the popularisation of math in South America. I first met Erika at the Gathering for Gardner recreational math, magic and art conference in Atlanta.

In the this video and the following, with the help of her brother, Eric, they explain the Mayan base-20 number system and how to do Mayan arithmetic.