A section of highway with a length of 20 kilometers has been repaired (4/5), how many kilometers are left to be repaired.
修一段长为20千米的公路，已修(4/5)，还剩多少千米没修．
<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">20 * (1/5)</gadget>
<output>4</output>

<result>4</result>