The scale of a map is (1/20000). The length of a rectangle measured on this map is 4 cm and the width is 2 cm. What is the actual area of the rectangle?
一幅地图的比例尺是(1/20000)，在这幅地图上量得一个长方形的长是4厘米，宽是2厘米，这个长方形实际的面积是多少．
<gadget id="calculator">1 / 20_000</gadget>
<output>1/20_000 = around 0.00005</output>

<gadget id="calculator">2 / (1/20_000) / 100</gadget>
<output>400</output>

<gadget id="calculator">4 / (1/20_000) / 100</gadget>
<output>800</output>

<gadget id="calculator">400 * 800</gadget>
<output>320_000</output>

<result>320_000</result>