SMP 11-16 is a mathematics course for secondary schools which emphasises the relationship between mathematics and the world around us. The course materials fall into two parts. Part 1, covering the first two years, consists mainly of topic booklets arranged in strands, which enable pupils to work at their own pace. Part 2, covering the next three years, consists mainly of four inter-related series of books for class use: Y(yellow), R(red), B(blue) and G(green). This book forms part of the Y (yellow) series, which is written for pupils of higher ability. It is an extension book, which can be used for individual study.