$A$ cone of height $9 \, cm$ with diameter of its base $18 \, cm$ is carved out from a wooden solid sphere of radius $9 \, cm$. The percentage of the wood wasted is

$A$ rectangular tin sheet is $12 \, cm$ long and $5 \, cm$ broad. It is rolled along its length to form a cylinder by making the opposite edges just touch each other. Then the volume of the cylinder is

$A$ hemisphere and a cone have equal bases. If their heights are also equal,the ratio of their curved surfaces will be

How many bricks,each measuring $250\, cm$ by $12.5\, cm$ by $7.5\, cm$,will be required to build a $5\, m$ long,$3\, m$ high and $20\, cm$ thick wall?

If the radius of a sphere is doubled,then its volume is increased by (in $\%$)

If the volume of a sphere is numerically equal to its surface area,then its diameter is ......... $cm$.