For a batch of books, if each pack contains 20 books, 18 packs should be bundled. If you want to bundle 15 packs, how many books per pack? (Solve with ratio)
一批书，如果每包20本，要捆18包．如果要捆15包，每包多少本？(用比例解)
<gadget id="calculator">20 * 18</gadget>
<output>360</output>

<gadget id="calculator">360 / 15</gadget>
<output>24</output>

<result>24</result>