Revision sheet · Mathematics

Permutations and combinations

Fundamental principle of counting: $N = mn$
Permutations of r things from n: $^{n} P_{r} = \frac{n !}{( n - r )!}$
Arrangements with alike things: $N = \frac{n !}{p ! q !}$
Combinations of r things from n: $^{n} C_{r} = \frac{n !}{r ! ( n - r )!}$
Pascal's rule: $^{n} C_{r} +^{n} C_{r - 1} =^{n + 1} C_{r}$