A car transports goods from the factory to the dock, travels 40 kilometers per hour when going there, arrives in 3 hours, and travels 60 kilometers per hour when returning. What is the average round trip speed.
一辆车从工厂运货物到码头，去时每小时行40千米，3小时到达，返回时每小时行60千米．往返的平均速度是多少．
<gadget id="calculator">40 * 3 * 2</gadget>
<output>240</output>

<gadget id="calculator">3 / 60</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">40 * (1/20)</gadget>
<output>2</output>

<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">240 / 5</gadget>
<output>48</output>

<result>48</result>