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A small difference (Posted on 2011-02-07) Difficulty: 3 of 5
Given a set a(1), a(2), a(3)...a(n), n>1.
Let P0 be the number of permutations of n elements, in which no element a(i) is in place i.

Let P1 be the number of permutations of n elements, in which exactly one element is in its original place i.

Show that ABS(P0-P1)=1.

When is P0-P1 positive?

No Solution Yet Submitted by Ady TZIDON    
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  Subject Author Date
SolutionSolutionHarry2011-02-09 21:56:33
Some ThoughtsExploration--no proofCharlie2011-02-07 14:35:47
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