It takes 20 days for team A to build a road and 30 days for team B to build it alone. How many days will it take for teams A and B to complete the joint repair?
修一条公路，单独修，甲队要20天完成，乙队要30天完成．甲乙两队合修，要多少天完成？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

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

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

<result>12</result>