Сыни ойлау18 мин

Combinations

Permutations vs combinations — does order matter? Then choose your formula.

Definitions

P(n,k) = \dfrac{n!}{(n-k)!}

C(n,k) = \binom{n}{k} = \dfrac{n!}{k!(n-k)!}

Ask one question: would swapping two of the chosen items count as a different outcome?

Combination

How many ways to choose a 3-person committee from 10 people?

Жауап: 120

Жаттығу

How many ways to seat 4 people in a row?

Жауап пен түсініктемені көру

Жауап: 24

Order matters — permutation $4! = 24$ .