A job can be done by A alone in (3/5) hours and by B alone in 0.4 hours. If A and B work together, how many hours can the work be completed.
一项工作，甲单独做需(3/5)小时完成，乙单独做需0.4小时完成．如果甲、乙合做，那么多少小时就能完成这项工作．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / (3/5)</gadget>
<output>5/3 = around 1.666667</output>

<gadget id="calculator">1 / 0.4</gadget>
<output>2.5</output>

<gadget id="calculator">(5/3) + 2.5</gadget>
<output>4.166667</output>

<gadget id="calculator">1 / 4.166667</gadget>
<output>0.24</output>

<result>0.24</result>