Xiao Li rides a motorcycle up the mountain, travels 20 kilometers per hour, and reaches the top of the mountain in 3 hours. It only takes 2 hours to go down the mountain. Find the average speed of Xiao Li's round trip by motorcycle.
小李骑摩托车上山每小时行20千米，3小时到达山顶．下山只用2小时，求小李骑摩托车往返的平均速度．
<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">20 * 3 * (2/5)</gadget>
<output>24</output>

<result>24</result>