A project can be completed by A alone in 15 days, and by B alone in 10 days. How many days will the two teams work together to complete.
一项工程，甲单独做成15天完成，乙单独做成10天完成．两队合做多少天完成．
<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>