Earth dug out of a well 14 m across and 6 m deep is banked evenly all round the mouth of the well to make a level ring 2 m high. Find the width of the ring, in m. Take π = 22/7.

The well has radius 7 $m$, so the earth removed = $(22/7)\times 49\times 6=924m^3$. The bank is a ring of inner radius 7 $m$, outer radius $R$ and height 2 $m:(22/7)(R^2-49)\times 2=924$ gives $R^2-49=(924\times 7)/44=147$, so $R^2=196$ and $R=14m$. The width is the difference of the radii, 14 − 7 = 7 $m.(14m$ is the outer radius and 28 $m$ the outer diameter — neither is the width; 3.5 $m$ halves the answer by mixing a radius with a diameter.)