A's speed up the mountain is 2 kilometers per hour, and his speed down the mountain is 6 kilometers per hour. What is his average speed up and down the mountain?
甲上山的速度是每小时2千米，下山的速度是每小时6千米，他上下山的平均速度是多少？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">2 / (2/3)</gadget>
<output>3</output>

<result>3</result>