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Combinations

★★☆☆☆Middle School

📖Definition

A combination is the number of ways to select r items from n items without regard to order.

\binomnr = C(n, r) = (n!)/(r!(n-r)!)

Combination formula

\binomnr = \binomnn-r

Symmetry property

\binomnr = \binomn-1r-1 + \binomn-1r

Pascal's identity

예제 1

Find the number of ways to choose 3 representatives from 10 people.

예제 2

How many 5-card hands from a 52-card deck?

Binomial distribution

Sample selection

Key combinations

#조합#경우의수#combinations#counting