Chapter 13 : Surface Areas and Volumes The chapter transitions from simple shapes (learned in Class IX) to complex, real-world objects. Combination of Solids: Objects formed by joining two or more basic solids (e.g., a capsule is a cylinder with two hemispheres). Surface Area Principle: The total surface area (TSA) of a combined solid is the sum of the curved surface areas (CSA) of its individual parts that are visible. Volume Principle: The volume of a combined solid is simply the sum of the volumes of its constituent parts Essential Formulas :