A pile of 3 tons of coal, use up (4/5) of the total, what fraction is left?
一堆煤3吨，用去总数的(4/5)，还剩几分之几？
<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>

<result>1/5 = around 0.2</result>