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The perimeter of the Mathematical Pond is 25 1.2m, surrounded by five wide cement roads and a circle of railings on the outside. What is the area of cement road?
Circumference C=2πR=25 1.2

So r = 25 1.2/2π = 40m.

The area of the cement road is the area of the ring, that is

S=π(40+5)？ -πx40x40

=2025π- 1600π

=425π

= 1334.5㎡

The length of the railing is the perimeter of the periphery:

C = 2π (40+5) = 90π = 282.6m。

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