A ship travels 60 kilometers per hour from A to B, and then returns on the same route. If the average speed of the round trip is 80 kilometers per hour, how many kilometers per hour should it travel when returning.
一艘轮船从甲地到乙地每小时航行60千米，然后按原路返回，若想往返的平均速度为80千米/小时，则返回时每小时应航行多少千米．
<gadget id="calculator">2 / 80</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/40) - (1/60)</gadget>
<output>1/120 = around 0.008333</output>

<gadget id="calculator">1 / (1/120)</gadget>
<output>120</output>

<result>120</result>