Probability

Definitions for terms and vocabs

Sample Space (S)

The set of all possible outcomes of a survey or experiment (ex. all farmers)

Event (A)

A Subset of the Sample Space (ex. farmers in alabama)

n ( ex. n(S), n(A) )

number of outcomes

n(A and B)

number of the intersection of event A and B

Pr(A and B)

probability of the intersection of event A and B

Formula for the probability of an event

Pr (A) = n(A)/n(S)

symbol for ‘And”

upside down U

Symbol for “Or”

U

Formula for or and probability

A or B = A + B - A and B

Complement of event (prime)

The opposite of the event (A prime)

n(A) + n(A prime) =

n(S)

Pr(A) + Pr(A prime) =

1

A or B or C =

A + B + C - A and B - B and C - C and A + A and B and C

(A or B)^c =

A' and B'

Pr (B | A) =

Pr (A and B) / Pr (A)

De’Morgan laws

The complement of a intersection is the complement of a union

Definition of dependent

Event B is dependent on event A if Pr(B | A) does not equal to Pr(B | A')

Determine the independence of events

if Pr(A and B) = Pr(A)*Pr(B)