Q.If the radius of the base and the height of a cone are both doubled, then the volume of the cone becomes—? (a) 3 times (b) 4 times (c) 6 times (d) 8 times
Answer: D
Let’s assume the initial radius was \(r\) and now it is \(2r\). The initial height was \(h\) and now it is \(2h\). Let the new volume be \(V\) and the previous volume be \(v\).
\(\therefore\) \(\cfrac{V}{v}=\cfrac{\cfrac{1}{3}\pi (2r)^2.2h}{\cfrac{1}{3}\pi (r)^2.h}=\cfrac{8r^2h}{r^2h}=\cfrac{8}{1}\)
\(\therefore\) \(V=8\times v\)
So, the new volume is 8 times the original volume.
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