A project can be completed by team A alone in 20 days and by team B in 30 days. How many days will it take for Team A and Team B to cooperate?
一项工程，甲队单独施工要20天完成，乙队单独施工要30天完成．甲、乙两队合作，几天完成？
<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">1 / (1/12)</gadget>
<output>12</output>

<result>12</result>