In the figure below, $n$ congruent semicircles are drawn along a diameter of a large semicircle, with their diameters covering the diameter of the large semicircle with no overlap. Let $A$ be the combined area of the small semicircles and $B$ be the area of the region inside the large semicircle but outside the small semicircles. The ratio $A:B$ is $1:18$. What is $n$?

If the diameter of a semi-circular protractor is $14 \mathrm{cm}$, then find its perimeter.

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 circumference of a circle is $39.6 \mathrm{cm}$. Find its radius. (Use $\pi =\frac{22}{7}$)

In the figure, $ABCD$ is a square of side $14 cm. A, B, C \& D$ are the canters of four congruent circles such that each circle touches extremely two of the remaining three circles. If the area of the shaded region is $k c{m}^2$ then find the value of $k$.

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