The radius of the cylinder is made twice as large. How should the height be changed so that the volume remains the same?

The total surface area of a hemisphere is $41.58 \text{ cm}^2$. Find its curved surface area (in $\text{cm}^2$).

The portion of a ditch $48 \ m$ long, $16.5 \ m$ wide, and $4 \ m$ deep that can be filled with stones and earth available during the excavation of a tunnel, cylindrical in shape, of diameter $4 \ m$ and length $56 \ m$ is (Take $\pi = \frac{22}{7}$)

$A$ right circular cylinder is circumscribing a hemisphere such that their bases are common. The ratio of their volumes is

$A$ cone-shaped circular tent is $9 \, m$ high and the circumference of its circular base is $44 \, m$. How much air is contained in the tent? (in $m^3$) (Use $\pi = \frac{22}{7}$)

An inverted conical shaped vessel is filled with water to its brim. The height of the vessel is $8\, cm$ and the radius of the open end is $5\, cm$. When a few solid spherical metallic balls,each of radius $\frac{1}{2}\, cm$,are dropped into the vessel,$25\%$ of the water overflows. The number of balls is: