# NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.8 – Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q-9 Twenty seven solid iron spheres, each of radius and surface area are melted to form a sphere with surface area . Find the

1. Radius of the new sphere,
2. Ratio of

Solution:

When the spheres are melted the volume of molten material remains the same.

1. Volume of solid sphere of radius , Volume of the new sphere of radius … equation (2) , Since the volume must remain the same, therefore,
2. Required ratio of surface area,
3. =
4. or the ratio is

Q-10 A capsule of medicine is in the shape of a sphere of diameter . How much medicine (in ) is needed to fill this capsule?

Solution: Diameter of the spherical capsule , Therefore, radius (r) , Medicine needed for filling this capsule = Volume of this spherical capsule