A bookcase has s shelves with n books on each shelf, where
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27 Dec 2021, 13:55
Let's plug in numbers. Let's pick s to be 5 and s-1 to be 4, such that n is then 20.
Each of the five shelves have 20 books making 100 books in total. If one shelf is emptied and all the 20 books in it distributed equally among the remaining 4 shelves, each of the 4 shelves would be getting 5 more books (because 20 divided into 4 places is 5), to make the books they contain to be 25 each. To check the reasoning, note that as no new books are added, the total number of books must remain 100, and 4*25 = 100.
We can then quickly test the answer choices to find the one that would yield 25 as answer. Luckily in this case, the first option A yields that, and is the answer.
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