Xiaoliang's speed when going up the mountain is 2 kilometers per hour, and his speed when going down the mountain by the original road is 6 kilometers per hour. What is the average speed of his going up and down the mountain in kilometers per hour
小亮上山时的速度是每小时2千米，按原路下山时的速度是每小时6千米，他上、下山的平均速度是多少千米/小时
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/2) + (1/6)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">2 / (2/3)</gadget>
<output>3</output>

<result>3</result>