Uncle Wang spent 3 hours driving from place A to place B, traveling 50 kilometers per hour, and 60 kilometers per hour when returning. What is the average round-trip speed of Uncle Wang?
王叔叔开车从甲地到乙地一共用了3小时，每小时行50千米，返回时每小时行60千米，求王叔叔的往返平均速度是多少？
<gadget id="calculator">3 * 50</gadget>
<output>150</output>

<gadget id="calculator">150 / 60</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">3 + (5/2)</gadget>
<output>11/2 = around 5.5</output>

<gadget id="calculator">2 / (11/2)</gadget>
<output>4/11 = around 0.363636</output>

<gadget id="calculator">150 * (4/11)</gadget>
<output>600/11 = around 54.545455</output>

<result>600/11 = around 54.545455</result>