Number A is 80% of Number B, how much less is Number A than Number B
甲数是乙数的80%，甲数比乙数少多少
<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>

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