A person goes hiking on weekends. He travels 4 kilometers per hour when going up the mountain, and travels 6 kilometers per hour when returning the same way. What is the average speed of this person in kilometers per hour?
某人周末去爬山，上山时每小时行4千米，原路返回时每小时行6千米．此人往返的平均速度是每小时多少千米．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/4) + (1/6)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">2 / (5/12)</gadget>
<output>24/5 = around 4.8</output>

<gadget id="calculator">1 * (24/5)</gadget>
<output>24/5 = around 4.8</output>

<result>24/5 = around 4.8</result>