There is a tunnel on the Yuyi Expressway. It takes 300 days to be repaired by engineering team A alone, and 200 days to be completed by engineering team B alone. Now the two teams are working from opposite ends of the tunnel at the same time. How many days can the tunnel be opened up?
渝宜高速路上有一条隧道，由甲工程队单独修要300天打通，由乙工程队单独修要200天打通，现在两队同时从隧道两端相向开工，多少天可以打通隧道．
<gadget id="calculator">1 / 300</gadget>
<output>1/300 = around 0.003333</output>

<gadget id="calculator">1 / 200</gadget>
<output>1/200 = around 0.005</output>

<gadget id="calculator">(1/300) + (1/200)</gadget>
<output>1/120 = around 0.008333</output>

<gadget id="calculator">1 / (1/120)</gadget>
<output>120</output>

<result>120</result>