Description Week 1 - The Relationship Between Addition and Subtraction Week 2 - Challenge! Calculation King Week 3 - Number + □ Week 4 - Number - □ Week 5 - □ - Number Week 6 - Challenge! Calculation King Math Starts With Understanding the Principles Math is an abstract discipline 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 genuine understanding. At every stage, understanding the underlying principles matters most. A Shift in Math Education The era in which simply knowing how to get the right 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 something works and encourage students to think of multiple methods, but when students focus only on repetitive practice, they often forget the underlying principles and end up producing answers mechanically — leaving them unprepared to understand more applied problems. Calculation practice should be steady and consistent. Structured into 4 to 6 books according to each stage of preschool and elementary learning, this series allows children to study just 10 minutes a day, every day. Lessons on principles and various methods are presented in a fun way with illustrations, while practice sections offer variety, and review sections help children focus and consolidate what they've learned. With this manageable daily study routine, children will find their calculation skills improving steadily before they know it. In this revised edition, Wonrisem expands its video lectures and strengthens the principle-based learning process for upper elementary grades, making it even easier to understand core concepts and calculation methods, while reinforcing practice for a more complete learning experience. We hope Wonrisem can help ease parents' concerns about math and calculation learning.