A 50-kilometer-long highway has been repaired for the full length (4/5), how many kilometers are left?
一条50千米长的公路，已经修了全长的(4/5)，还剩多少千米．
<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">50 * (1/5)</gadget>
<output>10</output>

<result>10</result>