The principal conducts outdoor sports-climbing. From the foot of the mountain to the top of the mountain, he goes up the mountain at a speed of 4 kilometers per hour. After reaching the top of the mountain, he returns to the foot of the mountain at a speed of 6 kilometers per hour. Find the average speed of the round trip?
校长开展户外运动-爬山，从山脚到山顶，以每小时4千米的速度上山，到山顶后，又以每小时6千米的速度返回山脚，求往返的平均速度？
<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>