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Formulas
Probability Rules:
Complements A and AC: P(AC) = 1 – P(A)
P(A or B) = P(A) + P(B) – P(A and B)
P(A and B) = P(A)*P(B|A)=P(B)*P(A|B)
A and B are disjoint events i.e. mutually exclusive if P(A and B) = 0, they cannot occur at
the same time.
A and B are independent events if P(A)=P(A|B) or P(B)=P(B|A)
Discrete random variable: x
Probability distribution: 0 ≤ P ( x ) ≤ 1,
Mean: μ = ∑ xP ( x )
∑ P(x) = 1
Binomial random variable: x counts the number of successes in n independent trials
where the probability of success on any one trial is p
⎛n⎞
Probability function: P ( x ) = ⎜⎜ ⎟⎟ p x (1 − p )n − x x = 0,1,2, K , n
⎝ x⎠
Mean: μ = np , Standard deviation: σ = np(1 − p )
Normal random variable, y:
Mean: μ , Standard deviation: σ
y−μ
Standardize: z =
σ
Distribution of the sample proportion, p̂ :
Shape: approximately normal,
p(1 − p )
n
Mean: p , Standard deviation: SD( pˆ ) =
Standardize: z =
pˆ − p
SD( pˆ )
Distribution of the sample mean, y :
Shape: approximately normal,
Mean: μ , Standard deviation: SD( y ) =
Standardize: z =
σ
n
y−μ
SD( y )
1
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