A project can be completed by team A alone in 30 days, and the time spent by team B alone is (2/3) of team A. How many days did the two teams work together?
一项工程，甲队独做30天完成，乙队独做的时间是甲队的(2/3)．两队合作几天完成？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">30 * (2/3)</gadget>
<output>20</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/30) + (1/20)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / (1/12)</gadget>
<output>12</output>

<result>12</result>