A pool has been filled with (1/5) of the pool's water, how much water will be filled to be full.
一个水池已经灌了(1/5)池的水，还要灌多少水才满．
<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>