The librarian wants to put a batch of books into the bookcase. If they are all put into bookcase A, then 12 books are placed on each floor; if they are all put into bookcase B, then 15 books are placed on each floor; if they are all put into bookcase C , 20 books are placed on each floor. Now put the books in three bookcases, how many books can be placed on each floor on average.
图书管理员要将一批图书放入书柜，如果都放入书柜A，则每层摆放12本书；如果都放入书柜B，则每层摆放15本书；如果都放入书柜C，则每层摆放20本书．现将书放入三个书柜，则平均每层可摆放多少本书．
<gadget id="calculator">15 / 12</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">2 * 2 * (5/4)</gadget>
<output>5</output>

<gadget id="calculator">15 / 15</gadget>
<output>1</output>

<gadget id="calculator">2 * 2 * 1</gadget>
<output>4</output>

<gadget id="calculator">15 / 20</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">2 * 2 * (3/4)</gadget>
<output>3</output>

<gadget id="calculator">5 + 4 + 3</gadget>
<output>12</output>

<result>5</result>