Q.If the ratio of the radii of two vertical solid cylinders is 2:3 and the ratio of their heights is 5:3, then the ratio of their curved surface areas is 20:27.

Assume that the radii of the two solid cylinders are \(r_1, r_2\) respectively, and their heights are \(h_1, h_2\). Curved surface area ratio = \(2\pi r_1 h_1 : 2\pi r_2 h_2\) \(= \cfrac{r_1 h_1}{r_2 h_2}\) \(= \cfrac{r_1}{r_2} \times \cfrac{h_1}{h_2}\) \(= \cfrac{2}{3} \times \cfrac{5}{3} = 10 : 9\) \(\therefore\) the ratio of their curved surface areas is \(10:9\).
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