A basket of apples a kilogram, how many kilograms are left after selling all (1/5) of them.
一筐苹果a千克，卖出全部的(1/5)后还剩多少千克．
<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>