A right circular cylinder is just enclosed a sphere of radius $r$, then :

If radius of a right circular cylinder is increased by$10\%$, then by what percent its height should be decreased so that its volume remains unchanged.

The radius of a solid right circular cone increases by $20\%$ and its height decreases by $20\%.$ The percentage change in its volume is:

Each vertical face of square based vertical pillar of height $3$ $m$ has $7$ equal, semi – cylindrical surfaces in such a way that its horizontal cross – section is as shown in the figure.

If the radius of each semi circle is $10 cm$, the volume (in $m^3$) of the pillar so designed (taking $\mathrm{\pi }=\frac{22}{7}$) is