Counting Methods, Permutations and Combinations (Edexcel A-Level Further Mathematics): Flashcards

$120$

Divide out repetitions by their factorials

Add for different cases, multiply within a case

Choosing items where order is important

Choosing items where order does not matter

$\frac{n!}{(n-r)!}$

$\frac{n!}{r!(n-r)!}$

Order of choice is important

Order of choice does not matter

$n!$