The distance from Beijing to Shanghai measured on a map of China with a scale of 1:5,000,000 is 4.2 centimeters. What is the actual distance between Beijing and Shanghai?
在比例尺是1：5000000的中国地图上量得北京到上海的距离是4.2厘米．北京到上海的实际距离大约是多少千米？
<gadget id="calculator">1 / 5_000_000</gadget>
<output>1/5_000_000 = around 0</output>

<gadget id="calculator">4.2 / (1/5_000_000) / 100_000</gadget>
<output>210</output>

<result>210</result>