On the map of 1:400000, the distance from Beijing to Tianjin is 30cm. What is the actual distance from Beijing to Tianjin in km?
在1：400000的地图上，量得北京到天津的距离30cm，北京到天津的实际距离是多少km．
<gadget id="calculator">1 / 400_000</gadget>
<output>1/400_000 = around 0.000002</output>

<gadget id="calculator">30 / (1/400_000) / 100_000</gadget>
<output>120</output>

<result>120</result>