Description Week 1 - Making Tens and Adding Week 2 - Making 10 and Adding Week 3 - Challenge! Calculation King Week 4 - Subtracting from Teen Numbers Week 5 - Making Tens and Subtracting Week 6 - Challenge! Calculation King Math Starts with Principles Math is an abstract discipline that expresses relationships between concrete objects through numbers and symbols. This is the biggest reason children find math difficult. Math can only show its true power when it comes with genuine understanding. At every stage, understanding the underlying principles is the most important part of math. A Change in Math Education The era when simply knowing how to get the right answer was enough for math education is coming to an end. Rather than repeating a single method over and over, it's important for children to learn various ways of solving calculation problems. Textbooks teach why certain methods work and encourage students to think of different approaches, but when students simply repeat drills without understanding the principles behind them, they end up producing answers mechanically—leading to a lack of understanding when it comes to applied problems. Calculation practice should be steady and consistent, structured across 4 to 6 books according to each stage of preschool and elementary learning, allowing children to study just 10 minutes a day. This series presents principles and various problem-solving methods in a fun way using illustrations, offers varied practice, and finishes with focused, concentrated exercises. With this manageable daily study amount, consistent practice will lead to a noticeable improvement in calculation skills before you know it. The revised edition of Wonli Sem expands video lectures and strengthens the principle-based learning process for upper elementary grades, making it easier to understand principles, concepts, and calculation methods while reinforcing practice for a more complete learning experience. We hope Wonli Sem can resolve parents' concerns about their children's calculation studies.