The modules are written for teachers. They provide the mathematical background to enable teachers, together with other resources, to plan the development of topics in their classrooms. This module is related to Module 1: Number and Algebra: counting and place value - teacher guide, Module 5: Number and Algebra: using place value to write numbers - teacher guide, Module 7: Number and Algebra: addition of whole numbers - teacher guide and Module 8: Number and Algebra: subtraction of whole numbers - teacher guide.