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Probability

Shelving five books with two kept apart

countingpermutationsrestrictions

You arrange 55 distinct books in a row on a shelf, but two specific volumes are so heavy that they must not be placed next to each other.

How many arrangements keep those two books apart?

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DerangementsBalls and Bins and the Birthday ProblemBinomial Coefficients and Pascal's TriangleBurnside's Lemma and Polya CountingCatalan Numbers

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