Counting Principle & Permutations
Section: Statistics & ProbabilityBank code: STA-PRMGRE frequency: HighPro
1. Core Idea
Counting problems reduce to one question: does order matter?
- Order matters -> permutation (arrangements, rankings, seat orders, passwords).
- Order does not matter -> combination (committees, teams, handshakes — see the next capsule).
And underneath both sits the fundamental counting principle: if one choice can be made in m ways and a second independently in n ways, together there are m x n ways.
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