The distance from Beijing to Shanghai measured on a Chinese map with a scale of 1:2000000 is 42 centimeters. What is the actual distance between Beijing and Shanghai?
在比例尺是1：2000000的中国地图上量得北京到上海的距离是42厘米．北京到上海的实际距离大约是多少千米？
<gadget id="calculator">1 / 2_000_000</gadget>
<output>1/2_000_000 = around 0</output>

<gadget id="calculator">42 / (1/2_000_000) / 100_000</gadget>
<output>840</output>

<result>840</result>