A monk carries water from the bottom of the mountain to the top of the mountain at a speed of 6 kilometers per hour, and the speed of going down the mountain is 12 kilometers per hour, what is the average speed of his going up and down the mountain in kilometers per hour?
一个和尚从山下挑水到山顶的速度是6千米/时，下山的速度是12千米/时，那么他上、下山的平均速度是多少千米/时．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

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

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/6) + (1/12)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / (1/4)</gadget>
<output>8</output>

<result>8</result>