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The radius of the base of a right circular cylinder is increased by 20%. By what per cent should its height be reduced so that its volume remains the same as before?
Answer & Solution
Correct Answer:
Option
D
$$\eqalign{
& 20\% \to \frac{{ + 1}}{5} \cr
& V = \pi {R^2}h \cr
& R \to 5:6 \cr
& {R^2} \to 25:36 \cr
& \boxed{{R^2} \propto \frac{1}{h}}{\text{ If volume same}} \cr} $$
$$\frac{{11}}{{36}} \times 100 = 30\frac{5}{9}\% $$
$$\frac{{11}}{{36}} \times 100 = 30\frac{5}{9}\% $$
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