The original price of a commodity is 20 yuan, and it is sold at a 15% discount. How much is it cheaper?
一种商品原价20元，打八五折出售，便宜了多少元．
<gadget id="calculator">85 / 100</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">1 - (17/20)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">20 * (3/20)</gadget>
<output>3</output>

<result>3</result>