Wang Fen's family plans to travel to Guilin, which is 900 kilometers away, during the summer vacation. On a map with a scale of 1:20000000, what is the distance in centimeters between her home and Guilin?
王芬一家计划在暑假期间去距离900千米的桂林旅游．在一幅比例尺是1：20000000的地图上，她家与桂林的图上距离是多少厘米？
<gadget id="calculator">1 / 20_000_000</gadget>
<output>1/20_000_000 = around 0</output>

<gadget id="calculator">900 * 100_000 * (1/20_000_000)</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>