A section of road can be repaired by A alone in 5 days; B can be repaired alone in 7 days. After A first repairs for 2 days, the rest will be completed by A and B together. How many days will it take to complete.
一段路，甲单独修，5天修完；乙单独修，7天修完．甲先修2天后，剩下的由甲乙合修，还需多少天完成．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) * 2</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

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

<gadget id="calculator">(3/5) / (12/35)</gadget>
<output>7/4 = around 1.75</output>

<result>7/4 = around 1.75</result>