It takes 20 days for construction team A to complete the construction of a canal, and 30 days for construction team B. How many days will it take for the two teams to work together?
修一条水渠，甲工程队要20天完成，乙工程队要30天完成．两队合修要多少天．
<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>