The flour extraction rate of wheat is 80%, how many kilograms of wheat are needed to grind 640 kilograms of flour?
小麦的出粉率是80%，要磨出面粉640千克，需要多少千克小麦？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">640 / (4/5)</gadget>
<output>800</output>

<result>800</result>