The curved surface area of a hemisphere is $27.72 \text{ cm}^2$ and its volume is $19.404 \text{ cm}^3$. Find its radius in $\text{cm}$.

$2\, cm$ of rain has fallen on a $1\, km^2$ of land. Assuming that $50\%$ of the raindrops could have been collected and contained in a pool having a $100\, m \times 10\, m$ base,by what level would the water level in the pool have increased? (in $m$)

The radius of a cylinder is increased by $20 \%$,keeping its height unchanged. What is the percentage increase in its volume?

$A$ ball of lead,$4\, cm$ in diameter,is covered with gold. If the volume of the gold and lead are equal,then the thickness of gold is approximately (in $cm$).
$[$ Given $\sqrt[3]{2} = 1.259 ]$

$A$ sphere is melted to form a cylinder whose height is $4 \frac{1}{2}$ times its radius. What is the ratio of the radius of the sphere to the radius of the cylinder?

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: