A coat is 81 yuan after a 10% discount, how much cheaper than the original one?
一件大衣打九折后是81元，比原来便宜多少元？
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">81 / (9/10)</gadget>
<output>90</output>

<gadget id="calculator">90 - 81</gadget>
<output>9</output>

<result>9</result>