This book is an expansion of the previous book, GNU Octave Primer for Beginners. This book inherits the first two chapters of the latter but enhanced with additional details and two more chapters, one on numerical methods and another on application of Octave/Matlab to numerous chores and games. The book is applicable to both Octave and Matlab users. Added also are exercise problems and answers showing how to use Octave and Matlab to solve the problems. The source programs in the book are all easily transferable to user's computer by copy/paste from a companion website. Numerical methods introduced in this book are essence of numerical analysis. Although brief and mostly elementary, it also includes numerical solutions of ODE and PDE. The last chapter shows how to apply Octave/Matlab to both business and fun projects, including mortgage payment finder, dice game, Sudoku solution and plotting of fractals. More detail of the book is available at http: //octave.ismr.us