Draw a circular lawn on a plan with a scale of 1:400. The radius on the picture is 5 cm. What is the actual area of the circular lawn in square meters?
把一个圆形草坪画在比例尺为1：400的平面图上，图上半径为5厘米，这个圆形草坪的实际面积是多少平方米．
<gadget id="calculator">1 / 400</gadget>
<output>1/400 = around 0.0025</output>

<gadget id="calculator">3 / (1/400) / 100</gadget>
<output>12</output>

<gadget id="calculator">12 ** 2</gadget>
<output>144</output>

<gadget id="calculator">3.14 * 144</gadget>
<output>452.16</output>

<result>452.16</result>