The price of a commodity is first reduced by 10%, and on this basis, 10% of the selling price is returned. How much is it actually reduced?
一种商品先降价10%，在此基础上又返还售价的10%，实际降低了多少．
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">(9/10) * (9/10)</gadget>
<output>81/100 = around 0.81</output>

<gadget id="calculator">1 - (81/100)</gadget>
<output>19/100 = around 0.19</output>

<result>19/100 = around 0.19</result>