A project needs 12 days to be built by engineering team A, and 20 days to be built by engineering team B. How many days will it take for the two teams to build together?
一项工程，由甲工程队修建，需要12天，由乙工程队修建，需要20天，两队共同修建需要多少天？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(1/12) + (1/20)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">1 / (2/15)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>