Xiao Ming goes to climb a mountain. He travels 3 kilometers per hour when going up the mountain, and 5 kilometers per hour when going down the mountain along the original road. What is the average speed of Xiao Ming going up and down the mountain this time?
小明去爬山，上山时每小时行3千米，沿原路下山时每小时行5千米，小明这次上下山的平均速度是多少．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/3) + (1/5)</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">2 / (8/15)</gadget>
<output>15/4 = around 3.75</output>

<gadget id="calculator">1 * (15/4)</gadget>
<output>15/4 = around 3.75</output>

<result>15/4 = around 3.75</result>