A person travels from A to B by car, with an average speed of 30 kilometers when going there, and an average speed of 24 kilometers when returning, find the average round-trip speed.
某人乘车从甲地去乙地，去时平均速度30千米，返回时速度平均为24千米，求往返平均速度．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

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

<gadget id="calculator">1 / 24</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">(1/30) + (1/24)</gadget>
<output>3/40 = around 0.075</output>

<gadget id="calculator">2 / (3/40)</gadget>
<output>80/3 = around 26.666667</output>

<result>80/3 = around 26.666667</result>