A commodity, the original price is how many yuan, after the price increase of 10 yuan, the price is reduced by 10%, and the result is 99 yuan.
一种商品，原价多少元，加价10元后，在降价10%，结果卖99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">99 / (9/10)</gadget>
<output>110</output>

<gadget id="calculator">110 - 10</gadget>
<output>100</output>

<result>100</result>