The original price of a commodity is 300 yuan, and it is sold at a 10% discount. How much is the discount for each item.
一种商品原价300元，按九折出售，每件优惠多少元．
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">300 * (1/10)</gadget>
<output>30</output>

<result>30</result>