Question

The width of a circular road is 28 m. The area of inner circle is 39424m². Find the diameter of the outer circle.

Answer 1

Let the radius of the inner circle be r m.
Radius of the outer circle = R m
Width of the circular ring = 28 m
Radius of the outer circle = R m = (r + 28) m
Area of the inner circle = $\pi$r²
$$\begin{gathered} \Rightarrow 39424=\frac{22}{7}\times r^2 \\ \Rightarrow r^2=\frac{39424\times 7}{22}=12544 \\ \Rightarrow r=112\mathrm{m} \end{gathered}$$

Radius of the inner circle = 112 m
Radius of the outer circle = (r + 28) m = (112 + 28) m = 140 m
Diameter of the outer circle = 2R = 2(140) m = 280 m