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Discrete-Math · Counting

21 choose 3

21,\ 3

Step by step

  1. \binom{21}{3} = \frac{21!}{3!\,(21-3)!}

    Unordered selections: n! / (k! (n−k)!).

  2. = \frac{51090942171709440000}{6 \times 6402373705728000} = 1330

Reveal the answer
\binom{21}{3} = 1330