A ship travels from port A to port B, travels 20 kilometers per hour when going, and travels 30 kilometers per hour when returning, find the round trip speed of the ship.
一艘船从甲港到乙港，去时每小时行驶20千米，回来时每小时行驶30千米，求这艘船来回速度．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

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

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) + (1/30)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">2 / (1/12)</gadget>
<output>24</output>

<result>24</result>