To build a 300-meter-long road, it takes 7 days for team A to repair it alone, and 5 days for team B to repair it alone.
修一条长300米的路，甲队单独修需要7天，乙队单独修需要5天，两队合修多少天修完．
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/7) + (1/5)</gadget>
<output>12/35 = around 0.342857</output>

<gadget id="calculator">1 / (12/35)</gadget>
<output>35/12 = around 2.916667</output>

<result>35/12 = around 2.916667</result>