A commercial flight takes 3.8 hours to go back and forth between the two cities. The speed of the flight is 500 kilometers per hour and the speed of the return flight is 450 kilometers per hour. How many kilometers are the distance between the two cities? (Please use the knowledge you have learned to choose at least three methods to answer)
一架民航班机在两城之间往返一次3.8小时，飞去的速度为每小时500千米，飞回的速度是每小时450千米，两城相距多少千米？(请利用所学知识，选择至少三种方法解答)
<gadget id="calculator">1 / 500</gadget>
<output>1/500 = around 0.002</output>

<gadget id="calculator">1 / 450</gadget>
<output>1/450 = around 0.002222</output>

<gadget id="calculator">(1/500) + (1/450)</gadget>
<output>19/4_500 = around 0.004222</output>

<gadget id="calculator">3.8 / (19/4_500)</gadget>
<output>900</output>

<result>900</result>