A chemical factory used 500 tons of coal in July, and the amount of coal used in August was 20% less than that in July. How many tons of coal was used in August?
某化工厂七月份用煤500吨，八月份用煤量比七月份少两成，八月份用煤多少吨．
<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>