Xiaoya buys 5 exercise books and pays 5 yuan, and gets back 2.5 yuan. How much is each exercise book?
小亚买5本练习本付出5元，找回2.5元，每本练习本多少元？
<gadget id="calculator">5 - 2.5</gadget>
<output>2.5</output>

<gadget id="calculator">2.5 / 5</gadget>
<output>0.5</output>

<result>0.5</result>