Xiaoqiang walks up the mountain at a speed of 4 m/s and after school walks at a speed of 3 m/s. What is the average round-trip speed in m/s?
小强上山步行速度是4米/秒，放学步行速度是3米/秒，往返平均速度是多少米/秒．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/4) + (1/3)</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">2 / (7/12)</gadget>
<output>24/7 = around 3.428571</output>

<result>24/7 = around 3.428571</result>