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Probability

A row of seven with two friends together

countingpermutationsrestrictions

Seven students stand in a row for a photo. Two of them, Ana and Ben, insist on standing next to each other.

How many arrangements of the row satisfy this?

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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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