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RD Sharma Class 9 Chapter 21 Solutions (Surface Area and Volume of a Sphere)

RD Sharma Class 9 Maths Solutions Chapter 21 will help you improve your conceptual clarity of the chapter ‘Surface Area and Volume’. There are 13 questions in 21.1 and 32 questions in 21.2. The first exercise of RD Sharma Solutions Chapter 21 is based on the sphere. Here you can see an ample number of questions that are based on Total Surface Area, Curved Surface Area and Volume of Sphere and Hemisphere.

The first few problems in RD Sharma Class 9 book are quite easy. As you do them, you will become more confident in attempting the upcoming questions that have an intermediate difficulty level. RD Sharma Class 9 Maths Solutions Chapter 21 has hemisphere based questions since they are under the same exercise in the NCERT book. Also, the hemisphere is a part of the sphere only and has almost the same formulas. The 13 questions in 12.1 are based on finding areas. They have many daily life-based questions that make it interesting to solve. In the last few questions, there are reference diagrams available in the answer for better understanding. The second exercise has 32 questions that cover volume-based questions. Many spherical objects like the moon, iron balls and capsules are used.

It is advised to pick this book once you have thoroughly practised all the questions and examples from your NCERT textbook because this has some HOTS questions as well that can be tricky for you if you are underprepared with the basic questions. RD Sharma Class 9 Maths Solutions Chapter 21 has a slightly upgraded level, so it is quite natural to get stuck many times. So, whenever you are having any trouble, you can feel free to check out our Solutions and continue with your exam practice. It is highly beneficial to seek help from RD Sharma Class 9 Maths Solutions Chapter 21 by Instasolv so that you can find out your own mistakes and even cross-check the steps that you followed.

Important topics for RD Sharma Class 9 Maths Solutions Chapter 21 Surface Area and Volume

 

  • The surface area of the sphere is 4 π r2. The total surface area of the hemisphere is 3 π r2 and lateral surface area is 2π r2.
  • Radius is half of the diameter. So if you are given a D, then you can divide it by 2 and get R.
  • In the thickness based questions, you have to subtract the inner volume from outer volume.  It is better to club the two formulas by taking the common terms out of the bracket.
    • Denote the radius of the inner circle by ‘r’ or ‘r1’ and outer radius by ‘R’ or ‘r2’.
    • The volume of the sphere isπ r3 and the volume of a hemisphere is π r3.
    • In a few questions, you have to find out the slant height of the cone.
    • Value of π is 3.14 or. Use the one that can make your calculation easier.
    • The SI unit of area is unit2, and that of the volume is unit3.
    • In many questions, you will be required to split the figure into different parts and then find the area or volume.
    • Also, in a few questions, the formulas of other figures will be used. So, it’s better to know all of them.

 

  • The first exercise, i.e. 21.1, has 13 questions. 
  • In question 1, there are three parts in which you have to use the formula straightforwardly.
  • In the next question, the diameter is given, so you have to find the radius first and then use the formula as done in the first question.
  • Question 5th belongs to the hemisphere. You can refer to RD Sharma Class 9 Maths Solutions Chapter 21 if you have any doubt.
  • Question 7th and 8th are application-based. 
  • The last question of 12.1 is a bit lengthy. You have to find the area to be painted and its cost.
  • Exercise 12.2 has 32 questions in total. The first 4 questions are straightforward.
  • In the 5th question, numbers of bullets are to be found by dividing the volume of the cube and volume of each bullet.

     

  • In question 11 is equality-based. Here you have to notice that it is given that the volume of the hemispherical bowl is equal to the volume of the cylinder. So, equate these two formulas and substitute the values of given entities. Calculate it carefully, and you can obtain the height, H.
  • Question 14 is also equality-based.

     

  • In question 17, you have to find out the number of spheres. For that, you have to divide the volume of the cylindrical jar and volume of the iron sphere.
  • Question 23 is a bit tricky to understand. Here you have to find out the number of cones using the formula of volume. You can solve it by taking the number of cones as ‘x’.
  • Question 30 is thickness based. So you have to subtract the inner volume from the outer volume.  Remember that the outer radius will be the inner radius + thickness of the tank.
  • In the last question, it is asked to find out the ratio of the volume of the moon and the volume of earth.

Benefits of RD Sharma Class 9 Maths Solutions Chapter 21 Surface Area and Volume by Instasolv

RD Sharma Class 9 Maths Solutions Chapter 21 by Instasolv has been compiled with detailed and easy Solutions that can help you throughout your session. You can reach and refer to them at any time of the day. With RD Sharma Class 9 Maths Solutions Chapter 21 by Instasolv you don’t have to wait for your next Maths Class in your school or tuition to solve your doubts. You can take help from the book that is prepared by our qualified experts anytime, anywhere. 

  • All the questions in RD Sharma Class 9 Maths Solutions Chapter 21 by Instasolv are explained stepwise and the formula used is mentioned along.
  • There are more than enough questions to practice and polish your maths skills. 
  • You can refer Instasolv for the Solutions whenever you want. It is made to ensure that you don’t have to rely upon anyone else.
  • The questions are lined up as per the difficulty level. So you can get the hang of it, starting up with easy questions and slowly moving towards the trickier ones.
  • Practice all the questions from RD Sharma Class 9 Maths Solutions Chapter 21 once you are done with the NCERT book. This will help you score high.