Brain Teasers
Book Stacks
In the Bookulike bookshop, the assistants are preparing for a signing session by the internationally renowned economist Emma Chizzit, to launch her latest title 'Last of the Big Spenders.'
Copies are piled up on a flat table in four equal stacks. From one side, only 9 spines in each stack are visible because they are piled up alternately: in other words, any book lying on top of another will have its spine facing in the exact opposite direction to that of the book below it.
What is the least possible number of copies on the table?
Copies are piled up on a flat table in four equal stacks. From one side, only 9 spines in each stack are visible because they are piled up alternately: in other words, any book lying on top of another will have its spine facing in the exact opposite direction to that of the book below it.
What is the least possible number of copies on the table?
Answer
68 booksIf the bottom book on each stack has its spine showing, and the top one does too, that would give 17 books to a pile (s + showing, n = not: SNSNSNSNSNSNSNSNS). 17 x 4 = 68
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