When Xiao Ming climbs the mountain, the speed of going up the mountain is 4 kilometers per hour, and the speed of going down the mountain is 6 kilometers per hour. Xiao Ming's average speed up and down the mountain is how many kilometers per hour.
小明登山时上山的速度为每小时4千米，下山的速度为每小时6千米．小明的上下山的平均速度每小时行多少千米．
<gadget id="calculator">1 + 1</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>