The ratio of radii of two spheres is $3: 5$. Then,the ratio of their surface areas is $\ldots \ldots \ldots$.

$A$ metallic cylinder with radius $15\, cm$ and height $20\, cm$ is melted and recast to produce identical balls with radius $3\, cm$. Find the number of balls produced.

The volume of a hemisphere with diameter $1 \, cm$ is $\ldots \ldots \, cm^3$.

$500$ persons are taking a dip into a cuboidal pond which is $80 \, m$ long and $50 \, m$ broad. What is the rise of water level in the pond,if the average displacement of the water by a person is $0.04 \, m^3$? (in $cm$)

$A$ solid toy is in the form of a hemisphere surmounted by a right circular cone. The height of the cone is $4\, cm$ and the diameter of the base is $8\, cm$. Determine the volume of the toy. If a cube circumscribes the toy,then find the difference of the volumes of cube and the toy. Also,find the total surface area of the toy.

The volume of a cone is equal to: