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Tuesday, November 09, 2010

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Name: Kent

Location: Singapore

I am a really shy guy who hate crowds but love being with friends! I also enjoy a good laugh!!

Puzzle of the day from perplexus.info:
Alternating Differences (Difficulty: 3 of 5)

Let X₁, X₂, X₃, ..., X_n be a permutation of the integers 1,2,3,...,n.

Consider the sum:
abs(X₁-X₃) + abs(X₂-X₄) + abs(X₃-X₅) + ... + abs(X_n-2-X_n).

What is the mean value of this sum taken over all possible permutations?

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