medium · GMAT Quant
A library organizes its 'New Arrivals' shelf with a sequence of 4 books. Each book on this shelf is covered with a dust jacket of one of 7 distinct colors.
If the librarian mandates that no two adjacent books can have the same color dust jacket, how many unique color sequences are possible for the 4 books?
- 1,512
- 2,401
- 1,296
- 840
- 252
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