A project can be completed in 10 days if team A works alone; if team B does it alone, it can be completed in 15 days. Now that the two teams cooperate, how many days can this project be completed?
一项工程，如果甲队独做，10天可以完成；如果乙队独做，15天可以完成．现在两队合作，几天能完成这项工程？
<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>