Question

The inner and outer diameters of ring I of a dartboard are 32 cm and 34 cm respectively and those are rings II are 19 cm and 21 cm respectively . What is the total area of the those two rings ?

Answer 1

Given: For Ring $I\Rightarrow$ $r_1=16$ and $r_2=17$

For Ring $II\Rightarrow$ $r_1=9.5$ and $r_2=10.5$

We have
Area of ring $I$ $=$ $(\pi \times {17}^2-\pi \times {16}^2)c{m}^2$

$=\frac{22}{7}\times ({17}^2-{16}^2)c{m}^2$

$=\frac{22}{7}\times (17+16)(17-16)c{m}^2$

$=\frac{22}{7}\times 33c{m}^2$

Area of ring II $=(\pi \times {10.5}^2-\pi \times {9.5}^2)c{m}^2$

$=\pi ({10.5}^2-{9.5}^2)c{m}^2$

$=\frac{22}{7}\times (10.5-9.5)(10.5+9.5)c{m}^2=\frac{22}{7}\times 20c{m}^2$

Total area of two ring $=\frac{22}{7}\times 33+\frac{22}{7}\times 20c{m}^2$

$=\frac{22}{7}\times (33+20)c{m}^2=166.57c{m}^2$