There is a 15% discount on a commodity. It used to cost 90 yuan, but how much less is it now.
一种商品打八五折，原来要90元，现在要少用多少元．
<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">90 * (3/20)</gadget>
<output>27/2 = around 13.5</output>

<result>27/2 = around 13.5</result>