A person travels 4 kilometers per hour uphill and 6 kilometers per hour downhill, what is the average number of kilometers this person travels up and down the mountain per hour?
某人上山每小时行4千米，下山每小时行6千米，这个人上下山平均每小时行多少千米．
<gadget id="calculator">1 * 2</gadget>
<output>2</output>

<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>

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