A wire is 20 meters long, after subtracting 80% of the total length, how many meters are left?
一根铁丝长20米，减去全长的80%后，还剩多少米．
<gadget id="calculator">80 / 100</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>