To process a batch of machine parts, Uncle Wang processes (1/20) every day, and Uncle Li processes (1/30) every day. If the two cooperate to process these parts at the same time, how many days can they finish processing?
加工一批机器零件，王叔叔每天加工(1/20)，李叔叔每天加工(1/30)，如果两人合作，同时加工这批零件，多少天能加工完？
<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>