Mr. Li won a grand prize of 500,000 yuan and received 400,000 yuan after paying the personal income tax. What is the tax rate of the personal income tax?
李老师中了50万大奖，缴完个人所得税后得款40万元，问该个人所得税的税率是多少．
<gadget id="calculator">50 - 40</gadget>
<output>10</output>

<gadget id="calculator">10 / 50</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">(1/5) * 1</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>