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Answers for “乘法原理与排列有什么关系?”

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Dividing the permutation count by r!r! yields the number of unordered groups because each specific set of rr items can be arranged in r!r! different orders. Since combinations ignore internal order, all r!r! permutations of a single group correspond to just one combination.

Conditions: The selection is without repetition.; The items are distinct.; We are converting from ordered selections (permutations) to unordered selections (combinations).