Q166
ArithmeticGeometry & Mensuration
If per cent increase in radius of cylinder is 300, then volume of the cylinder changes by how much per cent? (Keeping height of the cylinder constant)
- a.1500%
- b.600%
- c.-600%
- d.None of the above
Answer: (A) 1500%
An increase of 300 per cent makes the radius 4 times the original. Volume of a cylinder is $\pi r^2 h$; with the height unchanged the volume becomes $4^2 = 16$ times, an increase of $(16-1)\times100 = 1500$ per cent. Shortcut for a quantity depending on $r^2$: $300+300+\tfrac{300\times300}{100} = 1500$. Option (B) 600 per cent is the trap of simply doubling the percentage.