It takes Uncle Li 20 days to dig a canal, and Uncle Wang 30 days to complete it. If the two cooperate, how many days can it be completed?
挖一条水渠，李伯伯需要20天完成，王伯伯需要30天完成，如果两人合作，几天可以完成？
<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>