Two masters and apprentices process a batch of parts, the master alone can complete it in 20 days, and the apprentice alone can complete it in 30 days. If the two work together, how many days will it be completed?
师徒二人加工一批零件，师傅单独做20天完成，徒弟单独做30天完成，若两人合作多少天完成？
<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>