Conan is going to climb a mountain. When he goes up the mountain, his speed is 2 kilometers per hour. When he reaches the top of the mountain, he goes down immediately. The downhill speed is 6 kilometers per hour. What is his average speed?
柯南要去爬山，他上山时速度是每小时2千米，到达山顶立即下山．下山的速度是每小时6千米．请问他的平均速度是多少？
<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>