For a section of road, the full length (4/5) has been repaired, and the unrepaired part is how much has been repaired.
一段路，已经修好全长的(4/5)，未修的是已经修好的多少．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / (4/5)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>