A cylindrical container has sufficient water to submerge a solid cubical object of its each edge a cm. If the radius of the container is r cm, the rise in level (h cm) of water in the container is :

1. $\sqrt{\dfrac{a^3}{πr}}$

2. $\dfrac{a}{\sqrt{πr}}$

3. $\dfrac{a^3}{πr^2}$

4. $\dfrac{πr^2}{a}$

A solid cylinder of radius R cm and height H cm is melted and recast into smaller identical solid cylinders of height h cm and radius r cm. The number of smaller solid cylinders obtained is :

1. $\dfrac{RH}{rh}$

2. $\dfrac{R^2H}{r^2h}$

3. R²H ÷ r²h²

4. $\dfrac{RH^2}{rh}$

The inner radius of a pipe is 2.1 cm. How much water can 12 m of this pipe hold ?

How many cubic meters of earth must be dug out to make a well 28 m deep and 2.8 m in diameter ? Also, find the cost of plastering its inner surface at ₹ 4.50 per sq meter.