The knitting factory inspects the products and randomly checks some woolen sweaters. 1491 pieces are qualified and 9 pieces are unqualified. Find the unqualified rate.
针织厂检验产品，抽查了一些羊毛衫，合格的有1491件，不合格的有9件，求不合格率．
<gadget id="calculator">1_491 + 9</gadget>
<output>1_500</output>

<gadget id="calculator">9 / 1_500</gadget>
<output>3/500 = around 0.006</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

<gadget id="calculator">(3/500) * 1</gadget>
<output>3/500 = around 0.006</output>

<result>3/500 = around 0.006</result>