Different Strategies (Leaving Cert Mathematics): Flashcards

Small sample spaces - to visualise and verify possibilities

Multiply the number of choices at each step

Arrangements (permutations) of $n$ distinct objects

$n! = n \times (n-1) \times \dots \times 1$

Arrangements where order matters

$P(n,r) = \frac{n!}{(n-r)!}$

Selections where order does not matter

$C(n,r) = \frac{n!}{r!(n-r)!}$

Solving problems with multiple overlapping groups

$3 \times 4 = 12$ combinations

$4! = 24$

$5 \times 3 \times 2 = 30$ outfits

$120$ ways