After a batch of grain is sold (1/4), another 500 kilograms is brought in, which is 80% of the original amount. How many kilograms did it have?
一批粮食，卖去它的(1/4)后，又运进500千克，这时是原来的80%，原有多少千克？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

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

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(4/5) - (3/4)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">500 / (1/20)</gadget>
<output>10_000</output>

<result>10_000</result>