The school plans to use 500 degrees of electricity in May, but actually saved 20%, how much electricity is actually used.
学校计划5月份用电500度，实际节约了20%，实际用电多少度．
<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">500 * (4/5)</gadget>
<output>400</output>

<result>400</result>