Find the area of a sector of circle of radius $21\, cm$ and central angle $120^{\circ}$. (in $cm ^{2}$)
The radius of a circular ground is $90\, m$. Inside it, a road of width $10\, m$ runs around its boundary. Find the area of the road. $(\pi=3.14)$ (in $m^2$)
Find the difference of the areas of a sector of angle $120^{\circ}$ and its corresponding major sector of a circle of radius $21\, cm .$ (in $cm^2$)
On a square cardboard sheet of area $784 \,cm ^{2}$, four congruent circular plates of maximum size are placed such that each circular plate touches the other two plates and each side of the square sheet is tangent to two circular plates. Find the area of the square sheet not covered by the circular plates. (in $cm ^{2}$)
The length of the minute hand of a clock is $5\, cm$. Find the area swept by the minute hand during the time period $6: 05$ $a.m.$ and $6: 40$ $a.m.$ (in $cm^2$)