A project can be completed in 20 days by A alone, and (2/3) can be completed by B alone in 20 days. If A and B cooperate, how long will it take to complete the project?
一项工程，甲独做20天可以完成，乙独做20天能完成这项工程的(2/3)，如果甲、乙合作需多长时间才能完成这项工程？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(2/3) / 20</gadget>
<output>1/30 = around 0.033333</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>