A project can be completed by team A alone in 30 days, team B alone in 20 days, how many days will it take for the two teams to work together?
一项工程，甲队独做30天完成，乙队独做20天完成，两队合做，多少天完成．
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

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

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

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

<result>12</result>