Two children's clothing factories, A and B, cooperate to produce a batch of children's clothing. Factory A alone takes 10 days to complete, and factory B alone takes 5 days longer than factory A to complete. How many days can the two factories cooperate to complete?
甲乙两个童装厂合做一批儿童装．甲厂单独做要10天完成，乙厂单独做比甲厂多用5天完成．两厂合做多少天可以完成？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

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

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

<result>6</result>