The circumference of a circle with radius $8.4\,cm$ is $\ldots \ldots \ldots \ldots cm$.

The wheels of a car have a diameter of $80\, cm$ each. How many complete revolutions does each wheel make in $10\, minutes$ when the car is travelling at a speed of $66\, km/h$? [Use $\pi = \frac{22}{7}$]

The radius of a circle is $12 \, cm$. Find its circumference and area $(\pi = 3.14)$.

Is it true that the distance travelled by a circular wheel of diameter $d \text{ cm}$ in one revolution is $2 \pi d \text{ cm}$? Why?

Nine circular designs are made in a square show-piece as shown in the diagram. If the radius of each circle is $21\, cm$,find the area of the region without design. (in $cm^2$)

In the figure,a circle is inscribed in a square of side $5 \, cm$ and another circle is circumscribing the square. Is it true to say that the area of the outer circle is two times the area of the inner circle? Give reasons for your answer.