The original price of "One Hundred Thousand Whys" is 500 yuan per set. After the 15% discount, how much is the discount.
"十万个为什么"原价每套500元，打八五折优惠后，优惠了多少元．
<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">500 * (3/20)</gadget>
<output>75</output>

<result>75</result>