A car travels from A to B at an average of 60 kilometers per hour when going there, and at an average of 70 kilometers per hour when returning. What is the average round trip speed of this car in kilometers?
汽车从甲地开往乙地，去时平均每小时行60千米，返回时平均每小时行70千米．这辆汽车往返的平均速度是多少千米．
<gadget id="calculator">13 / 42</gadget>
<output>13/42 = around 0.309524</output>

<gadget id="calculator">2 / (13/42)</gadget>
<output>84/13 = around 6.461538</output>

<result>84/13 = around 6.461538</result>