The car travels from A to B at 50 kilometers per hour, arrives in 18 hours, and then returns from B to A at 75 kilometers per hour. What is the average speed of the car going back and forth between A and B?
汽车从甲地到乙地，每小时行50千米，18小时到达，然后从乙地返回甲地，每小时行75千米．问汽车往返甲、乙两地的平均速度是多少？
<gadget id="calculator">50 / 75</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">18 * (2/3)</gadget>
<output>12</output>

<gadget id="calculator">18 + 12</gadget>
<output>30</output>

<gadget id="calculator">2 / 30</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">18 * 50 * (1/15)</gadget>
<output>60</output>

<result>60</result>