On a map with a scale of 1:1,000,000, the measured length from Beijing to Shanghai is 4.2 cm. Then, what is the actual distance in kilometers from Beijing to Shanghai?
在比例尺是1：1000000的地图上，量得北京到上海长度是4.2厘米，那么，北京到上海的实际距离是多少千米．
<gadget id="calculator">1 / 1_000_000</gadget>
<output>1/1_000_000 = around 0.000001</output>

<gadget id="calculator">4.2 / (1/1_000_000) / 100_000</gadget>
<output>42</output>

<result>42</result>