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permutations_and_combinations [2019/03/31 14:49] (current)
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 +====== Permutations and Combinations ======
 +
 +A factorial is the number of ways to arrange $k$ things in $k$ spots. ​
 +
 +$k * (k-1) * (k-2) * .. 1 = k!$
 +
 +Permutations are a way in which a set or number of things can be ordered or arranged in which the order is important.
 +
 +Combinations are a way in which a set of things can be arranged where order doesn'​t matter. ​
 +
 +When we have to select $k$ things from $n$ possibilities:​
 +
 +Permutation - order matters ​       - no  repetition = $P(n,​k)=\frac{n!}{(n-k)!}$\\
 +Permutation - order matters ​       - yes repetition = $n^k$\\
 +Combination - order doesn'​t matter - no  repetition = $C(n,k)= \frac{n!}{k!(n-k)!}$\\
  
  • permutations_and_combinations.txt
  • Last modified: 2019/03/31 14:49
  • (external edit)