If the same exercise book is bound with a batch of paper, and each book is bound with 20 pages, it can hold 600 books; if each book is bound with 30 pages, how many books can be bound?
用一批纸装订同样的练习本，每本装订20页，可装600本；若每本装订30页，可装订多少本？
<gadget id="calculator">20 * 600</gadget>
<output>12_000</output>

<gadget id="calculator">12_000 / 30</gadget>
<output>400</output>

<result>400</result>