The number B is 80% of the number A, and the number B is less than the number A ((())/(())).
乙数是甲数的80%，乙数比甲数少((())/(()))．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / 1</gadget>
<output>1/5 = around 0.2</output>

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