The correct answer is: 22 cm, 231 cm² Explanation: Let AB be the given arc subtending an angle of 60° at the centre. Here, r = 21cm and θ = 60° $\displaystyle \begin{array}{l}\text{Length of the arc ABC}=\dfrac{{2\pi r\theta {}^\circ }}{{360{}^\circ }}cm\\=\left( {2\times \dfrac{{22}}{7}\times 21\times \dfrac{{60{}^\circ }}{{360{}^\circ }}} \right)cm=\text{ }22cm\\\text{Area of the sector OACBO}=\dfrac{{\pi {{r}^{2}}\theta {}^\circ }}{{360{}^\circ […]

The correct answer is: 693 cm² Explanation: Since the ribs are equally spaced, so the angle made by two consecutive ribs at the centre =($\displaystyle \dfrac{360}{8}$​)° = 45° Area between two consecutive ribs = area of a sector of a circle with r = 42 cm and θ = 45° =($\displaystyle \dfrac{45}{3600}$ × $\displaystyle \dfrac{22}{7}$ ​× 42

The correct answer is: 9.625 cm² Explanation: Area of shaded region = $\displaystyle \dfrac{22×30°}{7×360°}$  × (7² − 3.5²) = 9.625cm²

The correct answer is: 17: 21 Explanation: We known that ratio of areas of two similar triangles is equal to the ratio of square of their corresponding heights. $\displaystyle \dfrac{ar(△ABC)}{ar . (△DEF)}$ = $\displaystyle \dfrac{(4)²}{(9)²}$ =  $\displaystyle \dfrac{16}{81}$ ​