Xiao Ming goes up the mountain and travels 5 kilometers per hour, rests for 1 hour at the top of the mountain, and then goes down the mountain along the same road, and travels 8 kilometers per hour when going down the mountain. Find the average speed of Xiao Ming going up and down the mountain.
小明上山每小时行5千米，到达山顶休息1小时后沿原路下山，下山每小时行8千米，求小明上下山的平均速度．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/5) + (1/8)</gadget>
<output>13/40 = around 0.325</output>

<gadget id="calculator">2 / (13/40)</gadget>
<output>80/13 = around 6.153846</output>

<gadget id="calculator">1 * (80/13)</gadget>
<output>80/13 = around 6.153846</output>

<result>80/13 = around 6.153846</result>