What is permutation
Arrangement where order matters / sequence is important
What is combination
A selection where order does NOT matter
When do we use permutations in probability
When an event depends on the order.
Codes, pins, digit sequence
 when do we use combinations in probability?
When the event depends on which items. Not their order.
Drawing cards, balls.
Permutations
Given N objects, how many ways can they be arranged in a sequence?
N!
The compliment of an event
The set of outcomes that does not happen
Permutation formula
P(n,r) =
n!
——
(n-r)!
Combination Formula
C(n,r)
n!
———
(n-r)! r!
Probability of an event =
Ways achieving desired outcome
————————————————
Total outcomes
Á
Opposite/ complement of A
Permutations with replacement allowed
n choices , r slots
n^r
Probability using complement
P(E) = 1 - Á
P(A ⋂ B)
Probability A and B
P(A ⋃ B)
Probability A or B
P(A | B)
Probability A given B
