In $\odot( O , 12)$, minor $\widehat{ ACB }$ subtends an angle of measure $30$ at the centre. Then. the length of major $\widehat{A D B}$ is $\ldots \ldots \ldots . . cm .$
$10\pi $
$11\pi $
$20\pi $
$22\pi $
The circumference of a circle with radius $8.4\,cm$ is $\ldots \ldots \ldots \ldots cm$.
In a circle with radius $42\,cm ,$ an arc subtends an angle of measure $120$ at the centre. Then, the area of the minor sector formed by that arc is $\ldots \ldots \ldots . . cm ^{2}$.
The ratio of radii of two circles is $4: 5.$ Then, the ratio of their areas is...........
The circumference of the wheels of a truck is $440\, cm .$ They make $250$ rotations per minute. Then, the speed of the truck is $\ldots \ldots \ldots \ldots km / h$.
Areas of two circles are equal. Is it necessary that their circumferences are equal? Why?