Fatty climbs a mountain with an average speed of 2 kilometers per hour. When he reaches the top of the mountain, he descends immediately. The average speed of his descent is 6 kilometers per hour.
小胖爬山，上山的平均速度是每小时2千米，到达山顶后立即下山，下山的平均速度是每小时6千米，小胖上、下山的平均速度是每小时多少千米．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<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>