The original price of a product is a yuan, and the price is reduced by 10% for promotion. After a period of promotion, the price is increased by 10% before being sold. After the price increase, the price of this product is a yuan.
一件商品原来售价是a元，降价10%进行促销，促销一段时间后又提价10%再出售，提价后这种商品的价格是多少a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">1 + (1/10)</gadget>
<output>11/10 = around 1.1</output>

<gadget id="calculator">(9/10) * (11/10)</gadget>
<output>99/100 = around 0.99</output>

<result>99/100 = around 0.99</result>