Question

The diameter of asphere is decreased by 20%. By what percent does its curved surface area are decrease.

Answer 1

answer=36%
curved area of a sphere

$4\pi \: r { }^{2}$

it can also be written as

$4 \: \pi \: \: {(\frac{d}{2}) }^{2}$

or

$\pi \: d {}^{2}$

So area(A) Is proportional to d²
fractional change in area = 1-(0.8)² = 0.36
% change in area = 0.36×100=36%