A car travels 60 kilometers at a speed of 20 kilometers per hour and returns at 30 kilometers per hour. What is the average speed of the round trip in kilometers?
一辆车以每小时20千米的速度行完了60千米路程，回来时每小时行30千米，往返全程的平均速度是多少千米？
<gadget id="calculator">60 * 2</gadget>
<output>120</output>

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

<gadget id="calculator">60 / 30</gadget>
<output>2</output>

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

<gadget id="calculator">120 / 5</gadget>
<output>24</output>

<result>24</result>