Coal production in February was 420 tons, 20 tons more than 80% in January. How much coal is produced in January?
2月份产煤420吨，比一月份的80%多20吨．一月份产多少煤？
<gadget id="calculator">420 - 20</gadget>
<output>400</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">400 / (4/5)</gadget>
<output>500</output>

<result>500</result>