The road from the bottom of the mountain to the top of the mountain is 6 kilometers long. Xiao Ming travels 2 kilometers per hour up the mountain and 3 kilometers per hour down the mountain. What is his average speed up and down the mountain at kilometers per hour?
从山底到山顶的公路长6千米，小明上山每小时行2千米，下山每小时行3千米，他上下山的平均速度是每小时千米？
<gadget id="calculator">6 + 6</gadget>
<output>12</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">6 / 3</gadget>
<output>2</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">12 / 5</gadget>
<output>12/5 = around 2.4</output>

<result>12/5 = around 2.4</result>