It takes 10 days for a project to be completed by engineering team A alone, and it takes 15 days for construction by engineering team B alone. How many days will it take for the two teams to work together?
一项工程，由甲工程队单独施工，需10天完成；由乙工程队单独施工，需15天完成．两队共同施工，需要多少天完成？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</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>