A road is 800 meters long, 20% of which has been repaired, how many meters are left to be repaired.
一条路长800米，已修20%，还剩多少米没修．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">800 * (4/5)</gadget>
<output>640</output>

<result>640</result>