Question

The radii of two cylinders are in the ratio 2 : 3 and their heights are in the ratio 5 : 3. The ratio of their curved surface area is
(a) 2 : 5
(b) 8 : 7
(c) 10 : 9
(d) 16 : 9

Answer 1

(c) 10 : 9

Suppose that the radii of the cylinders are 2r and 3r and their respective heights are 5h and 3h.
Then, ratio of the curved surface areas = $\frac{2\mathrm{\pi }\left(2r\right)\left(5h\right)}{2\mathrm{\pi }\left(3r\right)\left(3h\right)}$=10 : 9