On Sunday, Xiaohong goes to climb the mountain. The speed of going up the mountain is 2 kilometers per hour, and the speed of going down the mountain is 3 kilometers per hour. Find her average speed up and down the mountain.
星期天小红去爬山，上山的速度是每小时行2千米，下山原路返回，速度为每小时行3千米．求她上、下山的平均速度．
<result>2.4</result>