For a pile of coal, (1/5) of the total amount is used up, and ((())/(())) of this pile of coal remains.
一堆煤，用去总数的(1/5)，还剩这堆煤的((())/(()))．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<result>4/5 = around 0.8</result>