When constructing a section of road, the ratio of the repaired to the unrepaired is 3:4, what is the proportion of the unrepaired part of the total length
修一段公路，已修的与未修的比是3：4，未修的占全长的多少
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>