On a map with a scale of 1:200,000, the distance between Huichang and Ruijin is 20 cm. What is the actual distance between Zechang and Ruijin in kilometers?
在一幅比例尺1：200000的地图上，量得会昌和瑞金的图上距离为20厘米．则会昌和瑞金的实际距离是多少千米．
<gadget id="calculator">1 / 200_000</gadget>
<output>1/200_000 = around 0.000005</output>

<gadget id="calculator">20 / (1/200_000) / 100_000</gadget>
<output>40</output>

<result>40</result>