NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.8 – Part 3
Q7 Find the volume of a sphere whose surface area is .
Solution:
Consider radius of the sphere to be
We know that, surface area
Since we know radius r, volume is =
Q8 A dome of a building is in the form of a hemisphere. From inside, it was whitewashed at the cost of If the cost of whitewashing is per square metre, find the

Inside surface area of the dome.

Volume of the air inside the dome.
Solution:
We know that,

Inside of the building is whitewashed at the cost of

Rate of white washing is per square metre.

Therefore, inside surface area of the dome


Let, radius of the dome be , then surface area (which we know from I. above)
Volume of the air inside the dome = Volume of the dome. However, since we know the radius, we can now calculate the volume =