Xiaoxian climbs a mountain at a speed of 2 kilometers per hour. After reaching the top of the mountain, he immediately descends the same road at a speed of 6 kilometers per hour. Find the average speed of Xiaoxian going up and down the mountain.
小弦爬山，上山的速度是每小时2千米，到达山顶后立即从原路下山，下山的速度是每小时6千米，求小弦上、下山的平均速度．
<gadget id="calculator">3 / 1</gadget>
<output>3</output>

<result>3</result>