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
Solution:
(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 $=\frac{2 \pi(2 r)(5 h)}{2 \pi(3 r)(3 h)}=10: 9$
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