Gangsta Granny Mental Maths Games A collection of fun number games that will help children in Key Stages 1 or 2 with their mental maths! The numbers games are based on David Walliams best selling Gangsta Granny book. With 48 cards all beautifully illustrated by Tony Ross. A collection of fun mental maths games where players add, subtract or multiply to get the highest possible scores. Who know that learning could be so much fun!