A "Fairy Tale Book" is 25 yuan, buy 4 books and get one free, how much is the actual cost of each book?
一本《童话故事书》25元，买4本送一本，实际每本少多少元？
<gadget id="calculator">25 * 4</gadget>
<output>100</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">100 / 5</gadget>
<output>20</output>

<gadget id="calculator">25 - 20</gadget>
<output>5</output>

<result>5</result>