There is a grain field in Tianzhuang, which harvested 620 tons of wheat last year. Due to the drought last year, the output was 20% lower than that of the previous year. How many tons of wheat were harvested last year?
田庄有一块粮田，前年收小麦620吨，去年因干旱，比前年减产二成，去年收小麦多少吨？
<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">620 * (4/5)</gadget>
<output>496</output>

<result>496</result>