A garment factory receives a batch of orders. The first workshop alone takes 30 days to complete, and the second workshop alone takes 60 days to complete. If the two workshops work on these orders at the same time, how many days can they be completed?
服装厂接到一批订单，第一车间单独做需30天完成，第二车间单独做需60天完成，如果两个车间同时做这批订单，多少天可以完成？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/30) + (1/60)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / (1/20)</gadget>
<output>20</output>

<result>20</result>