For a project, team A will complete the task in 10 days alone, and team B will complete the task in 15 days alone. How many days can the task be completed if the two teams cooperate?
一项工程，甲队单独做要10天完成任务，乙队单独做要15天完成任务．如果两个队合作，多少天能完成任务？
<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>