It takes 10 days for team A to complete a project alone, but the work efficiency of team B is three times that of team A. If the two teams cooperate at the same time, how many days can they complete the project?
一项工程，甲队单独完成需要10天，乙队的工作效率是甲队的3倍，两队同时合作，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">(1/10) * 3</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(1/10) + (3/10)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / (2/5)</gadget>
<output>5/2 = around 2.5</output>

<result>5/2 = around 2.5</result>