On a map of China with a scale of 1:50000000, the measured distance from Beijing to Shanghai is 2.1 cm. What is the actual distance from Beijing to Shanghai in km?
在比例尺是1：50000000的中国地图上，量得北京到上海的距离是2.1cm，北京到上海的实际距离约是多少km．
<gadget id="calculator">1 / 50_000_000</gadget>
<output>1/50_000_000 = around 0</output>

<gadget id="calculator">2.1 / (1/50_000_000) / 100_000</gadget>
<output>1_050</output>

<result>1_050</result>