During the "Six Day" Children's Day, the bookstore held promotional activities, and the original price of 25 yuan "Fun Math" was only sold for 15 yuan. By what percentage is the price of the book reduced?
"六一"儿童节期间，书店搞促销活动，原价25元的《趣味数学》只卖15元．这本书降价了百分之几？
<gadget id="calculator">25 - 15</gadget>
<output>10</output>

<gadget id="calculator">10 / 25</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>