RD Sharma Class 8 Chapter 21 Solutions (Mensuration II Volumes Surface Area Cuboid Cube)

RD Sharma Class 8 Maths Solutions for Chapter 21 are prepared to help you easily solve the questions in the RD Sharma Solutions exercises of the chapter. The topics in this chapter include an explanation about volume occupied by a space region and different units of volume. You will also learn how to derive the formula for the volumes of a cuboid and a cube respectively. Surface areas of cuboid and cubes are also covered in this chapter in a detailed manner. You will be introduced to the difference between the lateral surface area and total surface areas of the cubes and cuboids.

There are 77 questions in all compiled together in 4 exercises. There is a diverse set of problems in these exercises from fill in the blanks problems related to the units of volumes and areas to simple formula-based mensuration problems. You will also get to solve complex word problems that involve the application of these topics in your daily lives. The exercise questions of RD Sharma Class 8 chapter 21 employ concepts of both, total surface area and lateral surface area. The exercises are arranged strategically in increasing order of difficulty level to help you gradually grasp the complex concepts of the topic.

RD Sharma Class 8 Maths Solutions Chapter 21 by Instasolv comply with the latest CBSE guidelines. These RD Sharma Solutions include step by step explanations and will help you understand the approach and procedure of solving the questions related to volumes and surface area of cubes and cuboids. Practising the questions given in the RD Sharma Maths Book will not only help you in CBSE exams but also in national level competitive examinations and olympiads.

Important Topics for RD Sharma Solutions for Class 8 Chapter 21: Mensuration II (Volumes and Surface Areas of a Cuboid and a Cube)


  1. Cube: A cube is a three-dimensional object which can be defined in an XYZ cartesian system. All the dimensions in a cube, that is, the length, breadth and height are of equal lengths. 
  2. Cuboid: A cuboid can be represented in the XYZ cartesian system. There are 6 faces in a cuboid where the opposite faces of the cuboid are equal and parallel to one another.

Surface Area


  • Cube


  1. The total Surface area of a cube with dimension l, area =6l2
  2. The curved Surface area of the cube is given as, area=4l2. Note that, in the lateral or curved surface area, we eliminate the top and bottom face of the cube.


  • Cuboid:


  1. The total surface area of a cuboid with the length, breadth and height as l, b, and h respectively is given as, area=2(lb+bh+hl).
  2. The curved surface area of the cube is given as, area=2h(l+b).



  • Cube: Volume of a given cube with the length l is given as volume=l3


  • Cuboid: Volume of a given cuboid of dimensions as l, b and h respectively, can be given as, volume=lbh

We can use these concepts in calculating the rates of construction or painting the walls in a house or elsewhere or fencing our gardens etc.

Exercise Discussion for RD Sharma Solutions for Class 8 Chapter 21: Mensuration II (Volumes and Surface Areas of a Cuboid and a Cube)

  1. There are 21 questions in exercise 21.1 which are completely formula-based covering surface area and volumes cubes and cuboids. You will also get to find the dimension of cubes and cuboids with other information given in the questions.
  2. 20 questions in exercise 21.2 are word problems based on volumes of cuboids. These questions also include true or false math problems in the end.
  3. The 17 questions in 21.3 are both word problems and the objective type formula-based questions on surface areas of cuboids. You will get to find the amount of sheet required for construction or number of bricks required for the construction of a wall etc.
  4. The last exercise 21.4 is based on miscellaneous questions. You will get to practice evaluation of costs of different construction activities and determination of dimensions of cuboidal and cubical shapes in these exercise questions.

Benefits of RD Sharma Solutions for Class 8 Chapter 21: Mensuration II (Volumes and Surface Areas of a Cuboid and a Cube) by Instasolv

  1. You will find the right source of reference in our RD Sharma Class 8 Maths Solutions Maths Chapter 21. 
  2. All the questions of the chapter are covered in detail at the Instasolv platform.
  3. By referring to the answers at Instasolv, you will get to clear your queries simultaneously while solving the exercises. This will help you in approaching the problems in your maths exam with strongly prepared core concepts.
  4. Lastly, Instasolv solutions are easily accessible and absolutely free in an easily downloadable format.