60 likes | 255 Views
STA107 Lectures 18 & 19 Negative Binomial Distribution. Bernoulli trial Experiment has 2 outcomes, success or failure, P(S) = p Define RV X; X is # Successes, x= 0 or x=1 E(X) = p Var (X) = p(1-p). Geometric Distribution Conduct iid Bernoulli trails until a S occurs
E N D
STA107 Lectures 18 & 19Negative Binomial Distribution Bernoulli trial Experiment has 2 outcomes, success or failure, P(S) = p Define RV X; X is #Successes, x= 0 or x=1 E(X) = p Var(X) = p(1-p)
Geometric Distribution • Conduct iidBernoulli trails until a S occurs • Define RV X; X = #Trials; x= 1, 2, 3, …. • pmf: • E(X) = 1/p • Var(X) = (1-p)/p2
Example An intersection you pass on the way to school has a traffic light that is green for 40sec and then amber or red for a total of 60sec. What is the probability that Friday is the first day the light is green for you this week? Ans: 0.05184
Negative Binomial Distribution • Conduct iidBernoulli trails until k Successes have occurred • Define RV X; X = #Trials; x= k. k+1, k+2, …. • pmf: • E(X) = k/p • Var(X) = k(1-p)/p2
Example An oil company conducts a geological study that indicates that an exploratory oil well should have a 20% chance of striking oil. What is the probability that the first strike comes on the third well drilled? Ans: 0.128 What is the probability that the third strike comes on the seventh well drilled? Ans: 0.049