In the given figure, the diameter of the biggest semicircle is $56 \mathrm{cm}$ and the radius of the smallest circle is $7 \mathrm{cm}$. The area of the shaded portion is

Four circular plates of the same size having a diameter $a$ units each are placed on the square mat such that each plate touch externally the other two as shown in the figure. The area of the shaded region is;

Find the area of shaded region in Fig.$4$, if $ABCD$ is a rectangle with sides $8 cm$ and $6cm$ and $O$ o is the centre of circle $\left(Take \pi =3.14\right)$

The perimeter of a square is found to be equal to the circumference of a circle. The ratio of the area of that square to the area of that circle would be:

A CCTV camera is placed on the top of a $24$ m high pole in such a way that traffic can be seen beyond $25$ metre of line of sight of it. Find the area of the Green patch around the pole.

Find the circumference of a circle whose area is $6.16 {\mathrm{cm}}^2$.

Let $AB$ be a sector of a circle with centre $O$ and radius $d.\angle AOB=\theta \left(<\frac{\pi }{2}\right)$ and $D$ be a point on $OA$ such that $BD$ is perpendicular$OA$. Let $E$ be the mid-point of $BD$ and $F$ be a point on the arc $AB$ such that $EF$ is parallel to $OA$. Then, the ratio of length of the arc$AF$ to the length of the arc $AB$ is