Description Week 1 - Addition of Three Numbers Week 2 - Subtraction of Three Numbers Week 3 - Addition and Subtraction of Three Numbers Week 4 - Challenge! Calculation Champion Week 5 - Calculating with Reordered Numbers Week 6 - Challenge! Calculation Champion Math Starts with Principles Math is an abstract subject that expresses relationships between concrete objects using numbers and symbols. This is the biggest reason children find math difficult. Math can only show its true power when it is accompanied by proper understanding. At every stage, understanding the underlying principles is the most important part of learning math. A Shift in Math Education The era in which simply knowing how to arrive at an answer was enough is coming to an end. Rather than repeating a single method over and over, it's important for children to learn a variety of problem-solving approaches even in basic calculation. Textbooks teach why things work the way they do and encourage students to think of multiple methods, but through simple repetitive practice, students often forget the underlying principles and end up producing answers mechanically — leading to a poor understanding when it comes to applied problems. Consistent calculation practice, organized into 4 to 6 books according to each stage of preschool and elementary learning, allows children to study steadily for just 10 minutes a day. Principles and various methods are introduced in a fun way with illustrations, practice is varied, and the final review sections are designed for focused mastery. With this manageable daily study load, you'll find that calculation skills improve noticeably before you know it. The revised edition of Wonli Sem includes expanded video lectures and strengthened principle-based learning for upper elementary grades, making it easier to understand principles, concepts, and calculation methods, while reinforced practice adds to the overall completeness of learning. We hope Wonli Sem can help resolve parents' concerns about their children's calculation skills.