Let us take the radius as = 10
Therefore the area of the circular region = \(pi * r^2\)

=\(pi *10^2\)
=100pi

Now the radius is decreased by 20 percent

i.e 10-(10 * 0.2) = 8, which is the new radius

Therefore area of the circular region with the new radius = \(pi * 8^2\)
=64pi

Therefore the area of the circular region decreased = \(\frac{(New - old)}{old}\) = \(\frac{(64pi - 100pi)}{100pi}\)= \(-36%\) (The value is negative because the percentage is decreased)
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