Q.If the volume ratio of two right circular cones is 1:4 and the ratio of their base radii is 4:5, then the ratio of their heights is—? (a) 1:5 (b) 5:4 (c) 25:16 (d) 25:64
Answer: D
Let the heights be \(h_1\) and \(h_2\), and the base radii be \(4r\) and \(5r\) respectively.

\(∴ \cfrac{1}{3} π(4r)^2 h_1 : \cfrac{1}{3} π(5r)^2 h_2 = 1:4\)
or, \(16r^2 h_1 : 25r^2 h_2 = 1:4\)
or, \(\cfrac{16h_1}{25h_2} = \cfrac{1}{4}\)
or, \(\cfrac{h_1}{h_2} = \cfrac{25}{64}\)
or, \(h_1:h_2 = 25:64\).

So, the ratio of their heights is 25:64.
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