On a map with a scale of 1:20000000, the distance between Nanjing and Beijing is measured to be 4.5 cm, so how many kilometers is the actual distance between Nanjing and Beijing?
在比例尺是1：20000000的地图上，量得南京到北京的距离是4.5厘米，则南京到北京的实际距离大约是多少千米．
<gadget id="calculator">1 / 20_000_000</gadget>
<output>1/20_000_000 = around 0</output>

<gadget id="calculator">4.5 / (1/20_000_000) / 100_000</gadget>
<output>900</output>

<result>900</result>