Statistics & Probability
Intermediate

Combinations

Number of ways to choose r items from n (order irrelevant).

Formula

(nr)=n!r!(n−r)!\binom{n}{r} = \frac{n!}{r!(n-r)!}

Variables

nTotal items
rChosen items

Example

C(5,2) = 10

Did You Know?

Combinations count selections where order doesn't matter — the math behind lottery odds.

combinatoricscombinations