My Book of Subtraction looks to build upon the key skills acquired in My Book of Simple Subtraction (2013); the eventual aim being to prepare children for higher-level mathematics by improving their basic subtraction skills.This title begins by practicing how to subtract numbers one to nine, before reinforcing this and extending the process to 20.Each Kumon workbook is based on the 'Kumon Method'- an educational philosophy that aims at unlocking the full learning potential of each individual child.