A refrigerator factory produced 20,000 refrigerators in September, and 0.1% of the refrigerators were unqualified after inspection. How many qualified refrigerators did this factory produce in September?
某冰箱厂九月份生产冰箱20000台，经检验有0.1%的冰箱不合格，这个厂九月份生产了多少合格的冰箱？
<gadget id="calculator">0.1 / 100</gadget>
<output>0.001</output>

<gadget id="calculator">1 - 0.001</gadget>
<output>0.999</output>

<gadget id="calculator">20_000 * 0.999</gadget>
<output>19_980</output>

<result>19_980</result>