Question

Find area enclosed by two concentric circles whose radius are3.5cm &7cm

Answer 1

$area\ enclosed = \pi( {7}^{2} - {3.5}^{2} ) \\ = \frac{22}{7} \times (49 - \frac{49}{4} ) \\ = \frac{22}{7} \times 49(1- \frac{1}{4} ) \\ = 22 \times 7 \times \frac{3}{4} \\ = \frac{231}{2} \\ = 115.5$