| 单词 | permutations and combinations |
| 释义 | permutations and combinations A combination is any subset of a particular set of objects, regardless of the order of selection. If the set consists of n objects, r objects can be selected giving n!/r!(n - r)! different combinations. This can be written nCr. A permutation is an ordered subset (i.e. attention is paid to the order of selection or arrangement) of a particular set of objects. If the set consists of n objects, r such objects can be selected to give n!/(n - r)! permutations. This is written nPr |
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