The original price of a commodity is 100 yuan, and the price is reduced by 10% twice in a row, what should the selling price be?
一种商品原价100元，连续两次降价10%后，售价应是多少元．
<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">100 * (9/10) * (9/10)</gadget>
<output>81</output>

<result>81</result>