If number A is 80% of number B, how much less is number A than number B?
如果甲数是乙数的80%，那么甲数比乙数少多少
<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>