The distance between A and B is 300 kilometers. A car travels from A to B and arrives in 6 hours. It only takes 4 hours to return. What is the average speed of the car going back and forth in kilometers per hour?
甲、乙两地相距300千米，一辆汽车从甲地开往乙地，6小时到达，返回只用了4小时，则汽车往返的平均速度是每小时多少千米．
<gadget id="calculator">6 + 4</gadget>
<output>10</output>

<gadget id="calculator">2 / 10</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">300 * (1/5)</gadget>
<output>60</output>

<result>60</result>