Xiaoxiao ran up the mountain at a speed of 3 meters per second. After reaching the top of the mountain, immediately go down the mountain at a speed of 5 meters per second according to the original road, and return to the starting point. What is the average speed of Xiaoxiao going up and down the mountain?
笑笑以每秒3米的速度跑步上山．到达山顶后立即按原路以每秒5米的速度下山，回到出发点．笑笑上、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>

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