It takes 15 days for Team A to complete a project alone, and 10 days for Team B to do it alone. How many days will it take for the two teams to cooperate?
完成一项工程，由甲队单独做需要15天，乙队单独做需要10天，两队合作需要多少天．
<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>