A copy of "Mathematics World" is priced at 6.40 yuan, which is 36% cheaper than a copy of "Fairy Tales". How much cheaper?
一本《数学大世界》的定价为6.40元，比一本《童话大全》便宜36%，便宜多少元？
<gadget id="calculator">36 / 100</gadget>
<output>9/25 = around 0.36</output>

<gadget id="calculator">1 - (9/25)</gadget>
<output>16/25 = around 0.64</output>

<gadget id="calculator">6.4 / (16/25)</gadget>
<output>10</output>

<gadget id="calculator">10 * (9/25)</gadget>
<output>18/5 = around 3.6</output>

<result>18/5 = around 3.6</result>