On a design drawing with a scale of 1:200, the side length of the square bottom of the building is measured to be 20 cm. What is the actual area of the building in hectares?
在一张比例尺是1：200的设计图上，量得建筑物正方形底面的边长是20厘米．这个建筑物的实际占地面积是多少公顷．
<gadget id="calculator">1 / 200</gadget>
<output>1/200 = around 0.005</output>

<gadget id="calculator">20 / (1/200) / 100</gadget>
<output>40</output>

<gadget id="calculator">20 / (1/200) / 100 / 10_000</gadget>
<output>1/250 = around 0.004</output>

<gadget id="calculator">40 * (1/250)</gadget>
<output>4/25 = around 0.16</output>

<result>4/25 = around 0.16</result>