It takes 20 days for Uncle Wang to dig a canal, but Uncle Li can dig this canal every day (1/30). How many days will it take for the two to work together?
挖一条水渠，王伯伯要20天，李叔叔每天可以挖这条水渠的(1/30)，两人合作，几天能挖完？
<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>