A garment factory receives a batch of orders. The first workshop alone takes 15 days to complete, and the second workshop alone takes 10 days to complete. If the two workshops make these orders at the same time, how many days can they complete.
服装厂接到一批订单，第一车间单独做需要15天完成，第二车间单独需要10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 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/15) + (1/10)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / (1/6)</gadget>
<output>6</output>

<result>6</result>