The dome of a building is in the form of a hemisphere. Its radius is $4.2 \, m$. Find the cost of painting it at the rate of ₹ $18$ per $m^2$. (in ₹)

In a cylinder,if the radius is halved and the height is doubled,the volume will be

Write True or False and justify your answer in each of the following:
The volume of the largest right circular cone that can be fitted in a cube whose edge is $2r$ is equal to the volume of a hemisphere of radius $r$.

The surface area of a sphere with a radius of $5 \, cm$ is five times the curved surface area of a cone with a radius of $4 \, cm$. Find the height and volume of the cone (take $\pi = \frac{22}{7}$).

Find the surface area of a sphere of diameter $3.5\,m$ (in $m^2$).

The radii of two cylinders are in the ratio $3:2$ and their heights are in the ratio $8:11$. The ratio of their volumes is....... .