An athlete rides a bicycle back and forth between A and B. The speed when going is 30 kilometers per hour, and the speed when returning is 20 kilometers per hour. Ask the athlete what the average speed is per hour. km?
一个运动员骑自行车在甲、乙两地之间来回走了一趟，去时的速度是每小时30千米，回来时是每小时20千米，问这个运动员去来的平均速度是每小时多少千米？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/30) + (1/20)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">2 / (1/12)</gadget>
<output>24</output>

<result>24</result>