Question:
The radii of two concentric circles are 19 cm and 16 cm respectively. The area of the ring enclosed by these circles is
(a) 320 cm2
(b) 330 cm2
(c) 332 cm2
(d) 340 cm2
Solution:
(b) 330 cm2
Let:
R = 19 cm and r = 16 cm
Thus, we have:
Area of the ring $=\pi\left(R^{2}-r^{2}\right)$
$=\pi(R+r)(\mathrm{R}-\mathrm{r})$
$=\left|\frac{22}{7} \times(19+16) \times(19-16)\right| \mathrm{cm}^{2}$
$=\left(\frac{22}{7} \times 35 \times 3\right) \mathrm{cm}^{2}$
$=330 \mathrm{~cm}^{2}$
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