There are 400 books, put them on 2 bookshelves on average, each shelf has 8 layers, how many books are placed on each layer on average?
现有400本书，把它们平均放在2个书架上，每个书架有8层，平均每层放多少本？
<gadget id="calculator">2 * 8</gadget>
<output>16</output>

<gadget id="calculator">400 / 16</gadget>
<output>25</output>

<result>25</result>