Put 720 books on average on 4 bookshelves, each shelf has 2 layers, how many books are placed on each shelf on average? (two methods)
把720本书平均放在4个书架上，每个书架有2层，平均每个书架每层放多少本书？(两种方法)
<gadget id="calculator">720 / 4 / 2</gadget>
<output>90</output>

<result>90</result>