Description Sangwigwon Yeonsan 960 is the starting point of math and approaches the essential skill of numbers and operations—needed across all areas of math—with a new philosophy and methodology. Through task-solving math problems that combine various situations, processes, and methods, it not only builds strong calculation skills but also develops higher-level mathematical thinking. Sangwigwon Yeonsan 960 will be a great support for children who get bored or tired of simple, repetitive calculation drills, children who need creative-thinking calculation practice beyond basic arithmetic, children aiming for in-depth curriculum-based calculation practice, children who need to think through math rather than mechanically solve problems, children who want to build a solid foundation rather than rush into excessive advanced learning, children preparing step by step from an early grade for gifted education programs, olympiads, or specialized schools, and indeed any child who loves math and wants to excel at it. [Book Composition] 6 books at the P level, 4 books each at levels A-D, 22 books total A1: 241-300, Numbers up to 100 A2: 301-360, Addition A3: 361-420, Subtraction A4: 421-480, Using Addition and Subtraction [Recommended Grade] Essential thinking-skills calculation workbook for top-performing 1st grade elementary students Table of Contents A3: 361-420, Subtraction Issue 1: Subtraction up to 10 Issue 2: Two-digit subtraction without borrowing (1) Issue 3: Two-digit subtraction without borrowing (2) Issue 4: One-digit subtraction with borrowing Answer Key