A batch of apples is 20% sold for the first time, and 100 kg more than the first time is sold for the second time, leaving 500 kg. How many kg are there in this batch of apples?
一批苹果，第一次卖掉20%，第二次比第一次多卖100千克，还剩下500千克，这批苹果共有多少千克？
<gadget id="calculator">100 + 500</gadget>
<output>600</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5) - (1/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">600 / (3/5)</gadget>
<output>1_000</output>

<result>1_000</result>