To build a canal, team A can build the full length (1/10) in 3 days, and team B can finish it in 20 days alone. If the two teams work together, how many days can they finish it? (Xiangshan County, Zhejiang)
修一条水渠，甲队3天可以修全长的(1/10)，乙队单独修20天可以修完，如果两队合修，多少天可以修完？(浙江象山县)
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) / 3</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>