Question

Find the area of circular ring whose external and internal radius are 21 cm and 14 cm respectively

Answer 1

$area = \pi(x {}^{2} - y {}^{2} )$

x is taken as external radius and y as internal radius

$= \frac{22}{7} (21 {}^{2} - 14 {}^{2}) \\ = \frac{22}{7} \times 35 \times 7 \\ = 770cm {}^{2} \: \: \: \: answer$

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