Deposit 1,000 yuan, the annual interest rate is 2.25%, how much after-tax interest can you get after one year.
存入1000元，年利率是2.25%，一年后可得税后利息多少元．
<gadget id="calculator">2.25 / 100</gadget>
<output>0.0225</output>

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

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1_000 * 0.0225 * 1 * (4/5)</gadget>
<output>18</output>

<result>18</result>