The ratio of the radii of two circles is $4: 5$. Then,the ratio of their areas is...........

The diameter of a circle with area $154\,cm^{2}$ is $\ldots \ldots \ldots . cm$.

The floor of a room has dimensions $5 \, m \times 4 \, m$ and it is covered with circular tiles of diameter $50 \, cm$ each,as shown in the figure. Find the area of the floor that remains uncovered by the tiles. (Use $\pi = 3.14$) (in $m^2$)

As shown in the diagram,$\overline{OA}$ and $\overline{OB}$ are two radii of $\odot(O, 35 \text{ cm})$ perpendicular to each other. If $OD = 12 \text{ cm}$,find the area of the shaded region. (in $\text{cm}^2$)

The area of a circle is $3850 \, cm^2$. In that circle,the length of an arc subtending a right angle at the centre is $\ldots \ldots \ldots \, cm$.

In a circle with radius $14 \, cm$,the area of the minor sector corresponding to minor $\widehat{ACB}$ is $77 \, cm^2$. Then,minor $\widehat{ACB}$ subtends an angle of measure $\dots$ at the centre. (in $^\circ$)