The water consumption in September is 20% less than that in August, and the water consumption in September is equivalent to that in August.
九月份的用水量比八月份节约了20%，九月份的用水量相当于八月份的多少．
<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>

<result>4/5 = around 0.8</result>