If the sown area of grain crops in a village is reduced by 20%, how much should the yield per hectare be increased to keep the total grain output unchanged?
某村粮食作物播种面积减少20%，要保持粮食总产量不变，每公顷产量需增加多少．
<gadget id="calculator">5 - 4</gadget>
<output>1</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>