Xiao Ming rides a bicycle from A to B, traveling 12 kilometers per hour, and immediately returns on the same road after arriving at B, traveling 15 kilometers per hour. What is the average speed of Xiao Ming's round trip by bicycle
小明骑自行车从甲地去乙地，每小时行12千米，到达乙地后立即按原路返回，每小时行15千米．小明骑车往返的平均速度是多少
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(1/12) + (1/15)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">2 / (3/20)</gadget>
<output>40/3 = around 13.333333</output>

<result>40/3 = around 13.333333</result>