The volume of a cylinder is $20 \pi \, cm^3$ and its height is $5 \, cm$. Then,the diameter of the cylinder is $\ldots \ldots \ldots \ldots \, cm$.

$A$ metallic sphere with radius $42\, cm$ is melted to cast $8000$ identical balls. Find the radius of these balls (in $cm$).

The barrel of a fountain pen,cylindrical in shape,is $7 \, cm$ long and $5 \, mm$ in diameter. $A$ full barrel of ink in the pen is used up on writing $3300$ words on an average. How many words can be written in a bottle of ink containing one-fifth of a litre?

$A$ cylindrical tank with radius $8.4 \,cm$ is closed at one end by a hemisphere. If the total height of the tank is $52.8 \,cm$,how many litres of petrol can it contain (in $.088$)? (in $litres$)

$A$ $20\, m$ deep well with diameter $7\, m$ is dug and the earth from digging is evenly spread out to form a platform $22\, m$ by $14\, m$. Find the height of the platform. (in $m$) [Take $\pi=\frac{22}{7}$]

Find the number of metallic circular discs with $1.5\, cm$ base diameter and height $0.2\, cm$ that must be melted to form a right circular cylinder of height $10\, cm$ and diameter $4.5\, cm$.