30 is 20% less than that.
30比多少少20%．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">30 / (4/5)</gadget>
<output>75/2 = around 37.5</output>

<result>75/2 = around 37.5</result>