The $CSA$ (Curved Surface Area) of a $1-$ rupee coin is given by the formula $\ldots \ldots \ldots \ldots .$

$A$ wall $24 \, m$ long,$0.4 \, m$ thick and $6 \, m$ high is constructed with bricks each of dimensions $25 \, cm \times 16 \, cm \times 10 \, cm$. If the mortar occupies $\frac{1}{10}$th of the volume of the wall,then find the number of bricks used in constructing the wall.

$A$ cylinder is closed at both the ends by hemispheres. The radius of the cylinder is $20 \, cm$ and the total height of the article is $80 \, cm$. Find the total surface area of this combined article. $(\pi = 3.14)$ (in $cm^2$)

$A$ solid piece of iron in the form of a cuboid of dimensions $49 \, cm \times 33 \, cm \times 24 \, cm$ is moulded to form a solid sphere. The radius of the sphere is (in $cm$):

How many cones with diameter $7\,cm$ and height $3\,cm$ can be produced by melting a metallic sphere with diameter $21\,cm$?

$A$ 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.