Assign a batch of books to three classes A, B, and C according to 3:2:5. It is known that class A is allocated 15 books. How many books are there in this batch?
把一批图书按3：2：5分配给甲、乙、丙三个班，已知甲班分给15本，这批图书一共有多少本．
<gadget id="calculator">3 + 2 + 5</gadget>
<output>10</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">15 / (3/10)</gadget>
<output>50</output>

<result>50</result>