A kind of toy is sold at 15% off for 17 yuan, which is how much cheaper than the original price.
一种玩具，打八五折出售是17元，比原价便宜了多少元．
<gadget id="calculator">85 / 100</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">17 / (17/20)</gadget>
<output>20</output>

<gadget id="calculator">20 - 17</gadget>
<output>3</output>

<result>3</result>