11. Permutation and Combination
This chapter focuses on permutations and combinations, fundamental concepts in combinatorics. It explores the definitions, formulas, and applications of these concepts, particularly emphasizing the distinctions between ordered and unordered selections. Additionally, the chapter discusses cases where repetitions are allowed and introduces combinatorial proofs to validate the formulas derived.
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Sections
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What we have learnt
- Permutations represent ordered arrangements of objects, with significant distinctions made when the order of selection matters.
- Combinations refer to unordered selections of objects, where the arrangement is irrelevant.
- Repetitions can be allowed in selections, affecting the number of possible permutations and combinations.
Key Concepts
- -- Permutation
- An ordered arrangement of objects where the sequence matters, denoted as P(n, r) for selecting r elements from n.
- -- Combination
- An unordered selection of objects where the sequence does not matter, denoted as C(n, r) or sometimes as (n choose r).
- -- Repetition
- The allowance for the same element to be selected multiple times in permutations or combinations.
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